- Startup founders almost by definition have unreasonable ambition -- a level of interest that exceeds their actual capacity.

- The best people to work with on a project are very dedicated to their commitments and are placed in positions where their dedication is a priority.

- People unfailingly place a higher priority on commitments that are existing, concrete, regular, place-oriented and are reinforced by the most social pressure from people they know well and interact with the most. (1)

So this is just what happens, I think.

I've totally seen this before, both been the person that had to say "no" (many, many times), "I guess I can try helping you out for an hour a day" (never enough) and "I guess I can help" (when a friend's technical co-founder was swamped for months at their day job - again, it's hard to replace a full-time commitment).

I really think that this was a good person to get with, they honestly wanted to do this, and they thought they could swing it if they made the commitment. But again, that's their ambition talking. Their dedication was stuck at their existing job. I can't imagine the stress this caused both of you and I hope you both move on wiser and more motivated from this.

1. This is why seemingly every company wants people to work on-site.