There exist two different ideas, which I will spell out here explicitly:
Sometimes, when someone engages in a course of action that I hear described in a particular way, I cannot comprehend the line of logic that would lead a person to do that. There is no emotional input I can conceive of that, through currently documented theories, would lead to that course of action making sense. Accordingly, I tend to suspect that these people must have some motivation that is beyond my comprehension, with one possibility being a thought disorder. Yet, when this is the case, my base assumption is just that that there is a reason, and I simply don’t have enough data to know what it is.
Then, there are times when I hear of a course of action that takes place, and I find the action distasteful, even disturbing, but as I think through how the person must have come to that decision or sequence of decisions, I can discern a clear pathway from input to behavior, though I would have hoped a person could make better choices with those inputs.
This latter scenario is extremely common for me, and the former happens sometimes as well.
However, I quite often hear other people seem to describe a third scenario, a scenario that I somehow cannot recall ever having encountered: the thing is so inexplicable that they just insist that whatever happened was unexplainable, and they “can’t understand why a person would do that” or similar phrasing.
This almost never happens for me.
Sometimes I have engaged in discussion hoping that I was just misunderstood, and that when the person said the third statement they were really just lazily or poetically describing one of the first two. But I’m not really sure, because I’ve engaged, and they typically argue that it’s not worth trying to understand. This is also a foreign concept to me. Apart from perhaps love, which is best enjoyed without too much dissection, I’m not really aware of anything not worth the effort to at least try to understand.
These I think are just some of the ways that my experience is maybe different from that of some other people.