Hmm, you know, I've always found naming the biggest disappointment in my life difficult to answer. It's because there are so many disappointing moments in life, that it's best not naming them.
But now I've pondered on it, and I guess what I can consider my biggest disappointment in life was not studying Fine Arts. I had two chances, in University of Santo Tomas and University of the Philippines Diliman. I had hoped to use these Fine Arts credits to get an art-related job and probably enjoy more than what I'm doing now. I had wanted to do comic books.
I may be a writer now, but what I really liked doing is to draw. I still like to write, but I miss drawing and art. I just have no time now since my writing job is the only source of income I have. But I'll still love drawing and keep a few sketch pads on the side to keep myself from rusting in my other craft.