Opportunities that present themselves to you are the consequence -- at
least partially -- of being in the right place at the right time. They
tend to present themselves when you're not expecting it -- and often
when you are engaged in other activities that would seem to preclude you
from pursuing them. And they come and go quickly -- if you don't jump
all over an opportunity, someone else generally will and it will vanish.
-- Marc Andreessen (http://blog.pmarca.com/)