Are users rational? It depends on what you mean by rational

Icon of a brain and a cog

It’s fashionable to dismiss rational choice theory out of hand. I’m a big fan of Daniel Kahneman, whose work has done so much to detail its limitations. But contrary to what you may have been told, aspects of rational choice theory can still be helpful in understanding the world. And I find it a useful way to think about user experience. You just need to know how to handle it.

Do you remember that year at high school when your science teacher said, “forget everything you learned last year”? We’d been taught a simplified version of the science. It expressed fundamental principles that helped you understand the basics. But to take your understanding further, you had to try to forget some of the assumptions from the simplified model.

I have come to think of rational choice theory is an equivalent for human behaviour. Under close scrutiny, there are many cases where it’s inadequate to explain what’s going on. But that doesn’t mean that all of the fundamental principles are wrong.

So when I hear someone say, “people aren’t rational”, I have to decode it. Because whether they’re right or not depends on exactly what is meant by ‘rational’.

An economist’s view of rationality

When most people use the word ‘rational’, they usually mean something like ‘sensible’, ‘predictable’ or ‘clear-headed’. But economists had something more specific in mind.

At its simplest, this economic description of decision making is a cost–benefit analysis. You will choose the action that will give you the greatest net benefit.

So there are essentially two reasons people will make a decision:

  • It will increase their benefits.
  • It will reduce their costs.

We are not talking here about only monetary benefits and costs. Feeling happier counts as a benefit. A cost might be extra effort required to think, or unnecessary time spent.

The link with human-centred design

A lot of human-centred design boils down to these two simple goals as well.

Consider Jakob Nielsen’s classic article, 10 usability heuristics for user interface design. Almost all of these could be summarised to one statement: “reduce the cost to the user”.

In fact, almost all of the ten heuristics are about reducing cognitive burden. If a user interface is difficult to use, we are costing them time, and we’re making them think too much.

Which reminds me of another classic user experience text, Steve Krug’s Don’t Make Me Think. This book title has become a core mantra of usability. Yet it also could almost be the most succinct description of rational choice theory.

Usability heuristics are all about removing barriers for our users — and reducing their costs.

Or, as Paul Boag said:

I don’t mean to be rude, but you are lazy! But don’t feel too bad, so am I. In fact we all are. It is one of the defining characteristics of being human. Our relentless march to ever more advanced technology is largely driven by our inherent laziness. We are always looking for new ways to do things faster and with less effort.

Benefits of user research

We don’t just have to think about costs though. User researchers can consider the other side of the cost–benefit equation as well.

When we discover users’ needs, we do so in part so that we can ultimately increase their benefits. Economists call this maximising utility. Normal people call it making people happy.

It turns out that user experience is a great cost–benefit equation.

Of course, there are limits to rational choice theory. A deeper understanding of human behaviour will always help us design better solutions for users.

But as a starting point, I find the cost–benefit analogy useful in thinking about how we can improve users’ experiences.

Brain icon by Fabio Rinaldi from the Noun Project


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