Let me ask you a question that might make you uncomfortable. When did you last not do something - not because you did not want to, but because the process was too much of a hassle? A grant application you abandoned halfway through. A complaint you never filed because the form had twenty fields. A parental leave entitlement you never claimed because the procedure defeated you.
That feeling has a name. In behavioural science we call it sludge. And once you know what it is, you see it everywhere.
Sludge is unnecessary friction that stops people from doing what is good for them. The term was coined in 2020 by behavioural economist Cass Sunstein as the direct counterpart to a nudge. Where a nudge makes desired behaviour easier, sludge makes it harder - not through prohibition, but through obstacles. The SUE Influence Framework helps diagnose sludge by making the hidden blockers in a behaviour chain visible.
What exactly is sludge?
The term was coined by Cass Sunstein in his 2020 book Sludge: What Stops Us from Getting Things Done and What to Do About It. Sunstein is the man who, together with Richard Thaler, popularised nudge theory. After years of researching how to steer people in the right direction, he began looking at the mirror image: how are people actually being held back?[1]
His conclusion was damning. Everywhere he looked, he saw sludge. In government services. In insurance. In banking processes. In healthcare systems. Everywhere there were steps, forms, waiting times and verification procedures that served no functional purpose but that prevented people from doing what was good for them.
Sludge does not work through prohibition or coercion. It works through exhaustion. Every extra form field, every extra step, every extra click increases the probability that someone gives up. And the people who give up most are typically not the people with the least motivation. They are the people with the least time, the weakest digital skills, or the smallest cognitive bandwidth to push through bureaucracy.
Sludge is not an accident. It is the result of designers who have never had to struggle through their own processes.
This is also precisely why sludge is so morally loaded. It disproportionately affects people who are already vulnerable. And it is rarely designed with malicious intent. It is the result of systems built without ever considering the cost of navigating them.
Three examples of sludge at work
The onboarding that exhausts new employees before day one is done
A large Dutch bank once asked us to look at why new employees were taking so long to complete their onboarding. The HR department had built a comprehensive programme: twelve modules, sixteen forms, eight approvals from different departments before anyone had access to all systems.
The average time before a new employee was fully operational: nineteen days. The most common complaint in exit interviews from people who left within their first year: “I felt overwhelmed before I even started.”
We ran a sludge audit. Of the sixteen forms, nine were asking for information that already existed in the system. Of the eight approvals, five were historical artefacts: introduced after an incident, never questioned since. Three of the twelve modules existed solely because a department had lobbied for visibility in the onboarding programme.
After redesign: four forms, three approvals, seven modules. Average onboarding time: six days. And satisfaction scores for new employees in their first month rose by twenty-eight per cent.
The expenses process that discourages employees
A mid-sized municipality had a remarkably low rate of expense claims for business travel. The HR manager read this as a positive sign: employees were consciously choosing not to claim in order to spare the organisation. That turned out to be a classic misattribution.
When we ran a small sample survey, a different picture emerged: sixty per cent of employees were not claiming because the expense form was too complicated, receipts had to be submitted in the correct file format, the manager had to approve the claim through a system nobody understood well, and the reimbursement timeline was unpredictable - sometimes two weeks, sometimes six.
The process made claiming twenty euros literally not worth the effort. But this had an unexpected side effect: employees who travelled regularly and consistently missed out on larger amounts began developing a quiet resentment. The feeling that the organisation worked against them rather than for them.
Sludge always carries a hidden emotional cost. It is not just about the behaviour that fails to happen. It is also about the trust that erodes each time someone hits a wall.
The leave request nobody understands
This is a story I hear with painful regularity in our training sessions. An employee is entitled to carer’s leave. She knows this. Her mother needs care. She looks up how to apply. She finds a PDF. The PDF refers to a form on the intranet. She cannot find the form. She asks her manager. The manager does not know the procedure. She calls HR. HR sends her an email with an attachment. The attachment is a form from 2019. She fills it in. It is rejected because the form has been replaced by a digital version. She starts again.
She never completes the application. She takes annual leave instead.
This is sludge in its most damaging form: a right that exists but becomes inaccessible through procedural obstruction. And the organisation does not know, because nobody tracks how many employees abandon the process before completing it.
Why sludge is so persistent: an IF analysis
To understand sludge, it helps to look through the lens of the SUE Influence Framework. The IF asks: which forces drive people towards the desired behaviour, and which forces keep them in their current behaviour?
Pains (what pushes people away from current behaviour): a real problem exists that motivates people to act. They want to claim leave, file expenses, submit a complaint. The motivation is present.
Gains (what pulls people towards the desired behaviour): the benefit is clear. The leave creates space for care. The expense claim returns money. The advantage exists and is tangible.
Comforts (what keeps people in current behaviour): doing nothing costs no energy. Giving up is the path of least resistance. Not completing the process is the comfortable choice when the alternative is ten complicated steps.
Anxieties (what holds people back from changing): the fear of doing it wrong, submitting a form that will be rejected anyway, or burdening a manager with a request they might not support. Sludge amplifies these anxieties by adding uncertainty to every step.
The insight is this: sludge amplifies the Comforts and Anxieties while making the Gains invisible. Even when the motivation is present, the blocker wins. The solution is therefore not to create more motivation. The solution is to remove the blockers.[2]
How to run a sludge audit
A sludge audit is conceptually simple, but requires honesty. You walk through the full process from the user’s perspective and ask three questions at every step.
Is this step necessary? Not: was this step ever useful, or: did someone ask for it. But: does this step serve a concrete, current, legitimate purpose?
Is the information we are asking for here already known? Surprisingly often, organisations ask for information they already have: names, addresses, employee numbers, previously submitted documents. Every time a user fills in information that already exists in a system, that is sludge.
What is the dropout rate at this point? This is the most revealing question, and the one that most organisations cannot answer because they do not measure it. If you do not know how many people abandon your process at step five, you do not know where your sludge lives.
The standard interventions after a sludge audit are familiar to anyone working in behavioural design: pre-filled forms, smarter defaults, fewer steps, clearer language, better error feedback, and - the most powerful of all - eliminating steps that simply are not needed.
Frequently asked questions
What is sludge in behavioural design?
Sludge is unnecessary friction that stops people from doing what is in their own interest. The term was introduced by Cass Sunstein in 2020 as the direct counterpart to a nudge. Examples include: complicated forms, unnecessarily many steps in an application process, or a cancellation procedure that has been made deliberately complex.
What is the difference between sludge and friction?
Friction is a neutral concept: it is the resistance in a system or process. Sludge is a specific, normative category: it is friction that is unnecessary and that stops people from doing something that is good for them. Friction can also be useful - a cooling-off period before a large purchase is friction, but not sludge.
How do you recognise sludge in an organisation?
Sludge reveals itself when you ask: why is someone not doing this, when it is clearly in their interest? If the answer involves process, forms, steps or confusion - and not a fundamental lack of motivation - you are most likely looking at sludge. A sludge audit starts by mapping the full customer or employee journey and marking every friction point.
Is all friction sludge?
No. Not all friction is sludge. A cooling-off period for an impulsive purchase, a confirmation step before a major financial decision, or an identity check at a bank are forms of deliberately designed friction that protect people. Sludge is specifically friction that serves no functional purpose and that stops people from doing something that is good for them.
How do you remove sludge from a process?
Start with a sludge audit: walk through the full process step by step from the user’s perspective and note every point where friction arises. Ask at each friction point: is this necessary? Does this serve a legitimate purpose? If the answer is no, it is sludge. Then apply behavioural design: pre-filled forms, smarter defaults, fewer steps, clearer language.
Conclusion
Sludge is arguably the most underrated problem in organisational design. It costs money, trust and human wellbeing - and it remains invisible as long as you only look at the behaviour that happens, not the behaviour that does not.
Want to learn how to diagnose and design out sludge? In The Art of Designing Behaviour and in the Behavioural Design Fundamentals Course, you learn to apply the Influence Framework and its tools to systematically identify and eliminate the hidden blockers in behaviour and processes.
PS
At SUE we believe that the most powerful interventions are not the most visible ones. A nudge that steers behaviour without people noticing. A default that makes the best choice the easiest choice. And removing sludge, so that the path to desired behaviour is finally clear. Removing sludge is not a technical project. It is an act of respect for the people who have to navigate your processes.
