http://www.paulgraham.com/words.html
I've written about at least two subjects I know well — Lisp hacking and startups — and in both cases I learned a lot from writing about them. In both cases there were things I didn't consciously realize till I had to explain them.
直到需要解释的时候，才明白理解得并不清楚。能够从写作过程中获得新的理解。