Startup 1 (HavenCo): I regret not being "incrementalist" enough -- should have had a plan for $200k, $500k, $1m, etc., not a plan for $5-10mm in spend. I'm still not sure if it would have ended up any differently, but it might have been technically more interesting along the way.

Startup 2 (Iraq): I regret not vetting employees, and on relying on dishonest/criminal people. This killed a $50-100mm business.

In both cases I regret not properly separating my personal and business fiances, such that I was broke (or ~$200k in debt) after each. I ended up having to do boring consulting for a couple years to stay above water, after each.

For Startup 3, I've set aside a year of personal money which I won't touch, and am only working with people I trust -- I pretty much picked this of 2-3 other opportunities based on the skills of people I know and trust. I'm going for outside investment, even though it isn't absolutely essential, to enforce greater financial/reporting/fiduciary discipline, and to get really smart people involved -- I don't think advise from someone who won't invest is worth anywhere near as much.