Flash for Money and Motivation
I agree with everything jtmb2 said. Being able to know people like playing your game and your providing something thats fun for people is great, that warm fuzzy feeling i guess...whatever the hell that is :P
If you start Flash straight off for money it's kinda a bit ridiculous as them people make cheap copies of things, kills the creativity side. As long as you like making games and put effort into them then it's great to make money, but the main reason is too see your stuff come alive and do what you enjoy :)
The main reason I do it is I have tons of ideas and I can use Flash to make the ideas in your head, see them come to life. It's great. Money is just the reason I hope I can keep making this stuff....because if i get a 9-5 job that sucks, your motivation dies and I have no energy to make Flash at night when you get back.
Motivation is the key....99% of people that say they wish they could do Flash can, it's just they gotta put time into it and the starting off is the hardest bit. If your determined, stick at it, do whatever you need to keep refilling your energy :) Usually 3/4 through your flash you lose interest (i do a lot) just grunt through the rest and you'll be proud!!
I think I talked about myself too much...