Ego Depletion

Kathy Sierra:¹

If our work drains a user’s cognitive resources, what does he lose? What else could he have done with those scarce, precious, easily-depleted resources? Maybe he’s trying to stick with that diet. Or practice guitar. Or play with his kids.

That one new feature you added? That sparkly, Techcrunchable, awesome feature? What did it cost your user?

Ego depletion is the idea that you only have a limited amount of self-control that you can "spend" each day. Every decision you make uses part of that limited resource and makes it harder for you to make good decisions; breaks "refill" your ability to make thoughtful (or any) decisions.

In their paper Extraneous Factors in Judicial Decisions, authors Shai Danzigera, Jonathan Levavb, and Liora Avnaim-Pesso note that the longer judges work, the more unfavorable rulings they make:

We find that the percentage of favorable rulings drops gradually from ≈65% to nearly zero within each decision session and returns abruptly to ≈65% after a break.

The New York Times has a good article on the topic.

Applications that force users to make decisions deplete that same resource. The needless setting in your app, or that unclear screen that requires users to think about what they're supposed to do, might actually mean that somebody stays in prison who should have been released.