This surprised me, but “why?” is generally not a good question to ask, at least not when the topic is someone’s emotions or personal life. I think it’s because, to a lot of people, emotions just are. They feel less like part of the mind and more like part of the environment.

I think we can add to this: Don't ask why someone did something if they were pretty clearly acting mindlessly -- or at least certainly don't make it sound like you're asking for a justification. (I suppose that last part applies to asking about doing anything the person realizes was stupid.) Or rather, only ask this if both:

1. They're sufficiently self-aware that they can recognize in retrospect what mindless processes screwed them up
2. They know that you are prepared to accept such an explanation (and are not asking them to justify what they know was stupid)