There is no need to explain why your character did something. If you ask somebody to read your work (another writer or reader) and they question a character’s motivation for doing something, don’t waste your time explaining why the character did it unless you need to work through HOW to show your character’s motivation for doing something because clearly you didn’t. Pointing out that in prior chapters/scenes you’d set up the so-called motivation doesn’t cut it. Or, simply say “thank you” and move on. Because if you so strongly believe you have all your ducks in a row, then clearly the person who posed the question will get it. Maybe I don’t get it, but I do know motivation when I see it. And I also know that writing is tough. Hell, critique is tough. But it’s all apart of the job.