If your UX asks the user to make choices, for example, even if those choices are both clear and useful, the act of deciding is a cognitive drain. And not just while they’re deciding… even after we choose, an unconscious cognitive background thread is slowly consuming/leaking resources, “Was that the right choice?”
If your app is confusing and your tech support / FAQ isn’t helpful, you’re drawing down my scarce, precious, cognitive resources. If your app behaves counter-intuitively – even just once – I’ll leak cog resources every time I use it, forever, wondering, “wait, did that do what I expected?”.
Every choice is a cost. It’s an utterly simple principle, but it makes me step back and reconsider a lot of design choices made, both professionally and in side projects.