I'm wrestling with this same question myself. I have never had any idea. For me I've started businesses when the external pressure of having a co-founder dictated that I should. Or, I'd be in a fit of passion-inspired development for a few weeks until it was time to talk to customers. I think the answer varies from person to person. It's hard to say what a good heuristic would be. We all operate with different heuristics.
For instance I now have a family, and starting a business would either take me away from family time, involve nights and weekends work, or involve quitting my day job (of which the bar is now very high).
For instance I now have a family, and starting a business would either take me away from family time, involve nights and weekends work, or involve quitting my day job (of which the bar is now very high).
If you find the answer, let me know!