How do you decide if another person would be a good co-founder?
lionhearted: Track record. What have they produced in the past? Do they tend to complete things they've worked, or die 90% of the way to the finish line (a really bad thing)?Have they had any fallouts/meltdowns? There will always be a "good reason" it happened. No one will say "Yeah, I was a prick, and a drag, and a pessimist, and the company/project/whatever collapsed largely because of me." Also beware the, "I was immature back then, but I've recognized what I did wrong, and I've improved." No they haven't. At least, not if their last gig was a failing.Past a certain age, the vast majority of people pretty much don't change very much at all, ever. And if they had changed, they'd have accomplished something they could show you. So look at track record - it doesn't lie.Beyond that, there's plenty of good advice and Paul Graham's written on this plenty. A very big one for me - do they read books? Yes, books, not blogs/social news/newspaper/magazines. Avid reader of books is always a huge plus. Knowledge and lessons from books are repeated into you many times over a few days to a couple months as you read, so it sticks more permanently than reading a smorgasbord of unrelated things.