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Chapter 8: Resource depletion and pressure

Everyone has a finite amount of time – we all die eventually. To add to this, we’re all generally rather busy while we’re alive: we spend most of our time working, sleeping and completing tasks that we don’t really want to, like tidying our bedrooms and filling in forms. We also have a limited amount of energy each day before the burden of cognitive load1 or cognitive friction2 makes us fatigued. When we get tired, we become less able to engage in difficult cognitive tasks, more likely to use shortcuts (cognitive biases) and more error prone.3

This simple insight can be used in an exploitative manner to wear us down and trip us up. Software doesn’t need food, sleep or rest. A tedious series of steps will not bother an inanimate piece of software, but it will bother the user on the receiving end. This means that making something difficult is an effective way of stopping people from doing costly things – like cancelling subscriptions, opting out of surveillance tracking or exporting data. The strategy of exploitative resource depletion is often called ‘sludge’.4 Cass Sunstein explains the problem of sludge in his book on the topic:

‘In all likelihood, your life has been made worse because of sludge—a ‘viscous mixture,’ consisting of frictions that prevent you from doing what you want to do or from going where you want to go. […] In many cases, sludge imposes economic harm. […] It hurts patients, parents, teachers, doctors, nurses, employees, customers, investors, and developers. It compromises fundamental rights, including the right to vote and the right to be free from discrimination on the basis of race and sex. It is a pervasive source of inequality. Sludge can also be an assault on human dignity. […] Kafka captures that; his novels depict a world in which people cannot navigate life or escape their predicament because of that viscous mixture. […] It hurts all of us, but if you are sick, old, disabled, or poor, or if you don’t have a lot of education, sludge is a curse.’
— Cass Sunstein, 2022

In deceptive patterns literature, exploitative sludge in the interface is typically referred to as ‘obstruction’5 or in some cases ‘roach motel’,6 but we’ll come to that later.

It’s easy to create sludge. A business can add lots of steps and interruptions to any process. They can make the user fill in long forms, and enter their password multiple times. If they want to go really far, they can force people to send a letter by post, compel them to go somewhere in person, or make them use a call centre that has a confusing menu and long call-waiting times. This tactic is common with newspaper subscriptions and gym memberships. Life is full of interruptions and competing priorities, which means that sludge can make subscriptions last a little longer than users intend, which counts as free revenue for the business.

The impact of just one extra step can be substantial. In one study, BIT worked with HMRC to send letters to thousands of British citizens, asking them to pay their tax bills. They sent two different letters. In the first letter, they pointed users to a webpage that required users to click a link to get to the tax payment form (an extra step); in the second, they pointed users to the tax payment form directly, with no extra step.

The impact of the extra step was notable, with 5.1 percentage points fewer people completing the task.7 It’s easy to imagine...

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Since 2010, Harry Brignull has dedicated his career to understanding and exposing the techniques that are employed to exploit users online, known as “deceptive patterns” or “dark patterns”. He is credited with coining a number of the terms that are now popularly used in this research area, and is the founder of the website He has worked as an expert witness on a number of cases, including Nichols v. Noom Inc. ($56 million settlement), and FTC v. Publishers Clearing House LLC ($18.5 million settlement). Harry is also an accomplished user experience practitioner, having worked for organisations that include Smart Pension, Spotify, Pearson, HMRC, and the Telegraph newspaper.