2) Make sure you are good at sales BEFORE you quit your job (and that you've sold stuff)
3) MOST businesses fail because they don't have enough revenue, not because of product or people.
Resources/ books:
* The E-Myth
* All the stuff written by the Basecamp guys
* Jim Collins books
* Creativity Inc
I absolutely second this, but I would add a crucial section 1.5.
1.5) Also secure a seed-round to kick-start your company to test the for market fit. Then hire a few employees.
If after the seed-round it is either profitable or succeeds in the market and gets more investment, then it makes sense to quit your job and work full time for the startup.
Friends, Family & Savings
Don't let startup cash kill your idea before you give it a chance. Creative people can test an idea for next to nothing.
"There are two reasons founders resist going out and recruiting users individually. One is a combination of shyness and laziness. They'd rather sit at home writing code than go out and talk to a bunch of strangers and probably be rejected by most of them. But for a startup to succeed, at least one founder (usually the CEO) will have to spend a lot of time on sales and marketing. [2]"
...
"[2] Thanks to Sam Altman for suggesting I make this explicit. And no, you can't avoid doing sales by hiring someone to do it for you. You have to do sales yourself initially. Later you can hire a real salesperson to replace you."