When I make a presentation, the most typical question I get from the audience is : why you do this? It is the hardest one to answer.
Whenever I start something new, the honest reason I can currently tell is "my whole body asks me to do it". Quite simple, but assuming that most of the people would be puzzled by this answer, I try to come up with an easy story, quoting my life experience. This easy story, however, won't convince me throughly, and I feel a bit guilty.
Sometimes I think about why explanation of one's motivation is that difficult. Perhaps one potential reason is that one's motivation is a complex mixture of various experiences one had in her/his life. One's motivation may only be understood as a whole, and explaining each motivation-shaping factor may drop something very crucial. If that is the case, to explain one's real motive would be a brain teaser.
Difficulty of verbalizing one's motivation does not mean that we ought to skip the question of "why you do this?". I believe only by throughly examining one's own reason, he / she can understand him/herself more profoundly and can make his /her discipline more solid.
Not to end the self-search journey, one should not deceive oneself by the easy story. Once I stop pursuing the goal, I won't be able to see the vast story inside your mind, and that is regrettable to me. It's more challenging than we usually think, but we can try.