Surely that depends on what kind of partnership we're talking about? But yeah, if you want to partner with someone you need to have the same drive. If you're trying to revolutionize the world, and he wants to do the lifestyle thing, you're going nowhere.
To an extent, of course it does. If the "partnership" is one person paying another person a salary, then it's a completely different situation than two or three people profit-sharing. If it's in-person it's a completely different situation than internet partnerships.
But I don't think you can afford to be complacent even if you think your situation is ideal. Sometimes people don't let you down because they're arseholes ( though sometimes they probably are ) sometimes it's just a case of "things happen". When you're going it alone, and you're depending on someone who is half way through their work, then their sister gets taken ill and they have to drop everything, it's little consolation knowing that he's a nice guy and would have done exactly the same thing if he was working at a supermarket or working for IBM.
I'm just saying that if you're concerned about the prospect of going it alone, it's less of a risk to go it truly alone than it is to rely on anyone, no matter how nice or how reliable they are.