I wanted to spend more time with my family.
WHAT!? Yes, really. I had just gotten married, just bought an apartment, my wife was about to have our first kid and I started a business so that I could work from home and be with them more. I start at 7.30am and finish at 4.30pm. I usually work a half day on the weekend, and occasionally allow myself to take a weekday off to take my family to the zoo, or go shopping or whatever it is we feel like doing.
We're not rich, and we're always keeping an eye on the budget, but in exchange I've spent every day of the first two years of my sons life with him. In may we'll have our second, and I hope to achieve the same for him (or her!).
It IS hard work. I DO have to be disciplined. But with a careful balance of contract work and "Startup" work, we're doing ok.
We may never hit it rich, but whenever I hear my son cracking up laughing, I can walk out and see why and join in. That's worth more than any startup will ever be worth.