It has been claimed on this site that the fundamental question of rationality is "What do you believe, and why do you believe it?".
A good question it is, but I claim there is another of equal importance. I ask you, Less Wrong...
What are you doing?
And why are you doing it?
Nitpicking, but this "doing" question can't possibly be of equal importance to the fundamental question of rationality, because answering the "Why are you doing it?" part obviously depends on you having come to terms with what you believe, and why you believe it.
That said, I think this "doing" question is fundamental as well, second in importance only to the Fundamental Question. Good post.
The "Why" in "why are you doing it" could be interpreted as "for what purpose," or "as a result of what causal chain." Neither of these, at first blush, appears all that fundamental or difficult--but perhaps there's another sense I'm missing.