I've been involved in start-ups and have been a partner in a couple.
I now have 3 kids and view my 8-6 job as an athlete views game day. I seek to perform at my highest level during work hours and then try to turn it off after. I don't miss it when I'm with my kids or my wife or friends. For me, there's more to life than work/job/running a business.
I've also come to the conclusion that I have 100% certainty of improving my kids lives through spending time with them. That time doesn't scale like running a startup, but it's guaranteed to be effective. I'll take those odds over the 1 in a million of running a startup, even if it's just improving 3 lives.