"Why are you using a QWERTY keyboard?" or "Why haven't you invested in stocks?" and you don't remember already considering this exact question and deciding it,

It think you mean: If I don't remember already considering the question "should I do X", Checking for a cached answer to the why question can just yield an answer to the wrong question.

You've got to rewrite the question _first_, then check to see if you know an answer to the right question.