Three Personality Traits of The Ideal Co-founder

After working with a lot of potential co-founders who didn't quite fit the bill, I've distilled the ideal co-founder down to three core characteristics:

1) Smart
2) Trustworthy
3) Hardworking

This may sound obvious, but the core problem is that a lot of seemingly great people only fulfill two of the three. Which means that they won't work out as your cofounder. I think that the definition of each characteristic is pretty self-explanatory, so I'll describe the trait combinations that don't quite work.

QUICK NOTE: These are caricatures. Everyone will probably have one or more of these to some extent. The thing that really matters is the magnitude of that extent, and how the flaw interacts with your personality.

Smart and Hardworking (But Inconsistent)
You meet this guy (or girl), and you can see the spark in his eyes. He has lots of interesting ideas, and is always in a rush to implement them. The quality of his work is high, and he seems like he is going places. But there is something about him that you just don't quite trust. Maybe it's something concrete (like constantly being late, or blowing you off inexplicably), or maybe it's just a feeling of unease in the pit of your stomach. Whatever the case, this isn't going to work. One day, this guy is going to sell you out when something better comes along. Or he's going to exploit your work and then use a loophole to con you out of your equity. Soak up everything you can get from this guy, but keep your eyes on the knife drawer

Hardworking and Trustworthy (But a Bit Inept)
Honestly, this combination is the hardest to ditch. This guy is sweet - he's obviously super-loyal, and he works tirelessly. But... his work isn't quite what you could have produced. When you give him a task that you could have finished in a day, he finishes it in three or four days. And he needs a lot of direction - the only way to guarantee that his work is top-quality is to hold his hand through all of it.

This guy could be a great employee at a larger company, but he just won't cut it as a cofounder. The startup needs to move fast, and everyone needs to contribute on a reasonably equal basis. Some cofounders will be unable to do the work that you do because they have a completely different set of talents, and that's fine. But, when there is a lot of overlap, you should feel like your cofounder is roughly equal to you, if not better in many respects.

Smart and Trustworthy (But A Bit Lazy)
You geninely enjoy being around this guy, and he has so many great ideas. He can think through literally anything - you're sure that you and he are toe-to-toe in the brains department. But he doesn't get that much done, unless you push him. I'm sorry to say it, but this guy is lazy. At a large company, he could be at home in the strategy department. But, at a startup, there are no strategy roles. Everyone needs to be building or selling the product at all times. There is no place for the non-self motivated. It's a tough world out there.

Conclusions?
So, something I've realized is that there is no perfect cofounder. Everyone has one or more of these flaws. They are either inconsistent, inept, lazy, or a combination of the above. As an aside, when I say inept and lazy, I'm talking about a lot of people who would be considered brilliant and hardworking in comparison to 95% of the people out there. It's important to be honest about everyone's flaws (including your own), and to find people whose talents complement your flaws. Maybe you are lazy, and can find a cofounder who is happy to do do your work. Or maybe you are inconsistent, and can find someone who is trustworthy and won't double-cross you (until you find someone better).

This is one major reason why the smart money in the startup world suggests that you date your cofounder before you take the plunge. After dating, joining, and even splitting from a bunch of cofounders, I can say that you need to tread carefully...