$100 Startup by Chris Guillebeau. So far the book is great, profiling folks like myself who started their own one-person business without many startup costs and without too much of an official business plan (the plan is...sell things!).
This quote in particular jumped out at me though, because I think a lot of creative people suffer from an affliction called perfectionism where they think either they aren't "prepared enough" or they want to get things "just right". In my humble opinion perfectionism can hold you back and prevent you from trying many things that you could be successful at, if only you gave them a chance without being perfectly prepared for any and all possibilities.
Now, I appreciate extremely well executed ideas, and I'm not advocating that you start up your own business without at least having an idea of what you'll need to learn to be successful, but I believe in most cases you can "learn on the job" so to speak (note: this is probably not true if you want to start your own skydiving business). That was definitely the case with me and Adobe Illustrator when I started up Concertina Press - I open up some of the files I made one year ago and it's like a tangled mess! (Clipping Mask? What's that?) BUT I would have never had the opportunity to hone my skills if I hadn't opened up a shop anyway so that people would buy invitations and I'd have a reason to learn more as I created new designs.
Anyway, so what's this all about? The takeaway message is, if you have a great idea, and it won't cost too much to try it out** - DO IT.
If it doesn't work out, boo, try something else - but if it does, great! Point is, you'll never know until you try.
*Ironic, because if you recall your history Friedrich Engels co-wrote "The Communist Manifesto" with Karl Marx...
**I do want to emphasize that...I'm talking small here...like selling your stuff on ebay, not like "I want to open a MULTINATIONAL EXPORT CORPORATION!"