I think context is important here. I don't think I am wrong in saying that most YC startups consist of 20-somethings, perhaps even in their low 20's. At this age few are truly prepared for the stress, conflict and issues that running a business could bring to the table. And, in this context, it is probably far better to have more founders rather than less.<p>I've been an entrepreneur ever since I can remember. And, retrospectively, I know that I did a lot of dumb things when I was younger. It takes a while to develop the business smarts, thick skin and, if you will, intestinal fortitude a business requires. I've experienced business issues as I got older that I know would have totally decimated me when I was younger. You are simply not prepared for that sort of thing. Particularly things like impending catastrophic failure, when you need to be mentally and emotionally in your strongest mode.<p>Barely-out-of-teenage-years entrepreneurs (not meant with disrespect at all, just chronological fact) need a support system in order to stay the course, learn and not derail. That's why I think that in these cases the multiple founder "rule" is probably a very good idea.<p>I would say that older solo founders with previous skin in the game are probably a good bet (all else being equal). One young founder thrown into the jungle that business can become is probably a formula for almost certain failure.<p>While, of course, there are always exceptions to every rule, I do think that what I am saying is a reasonable characterization of the problem.