If you're a programmer, and you're relatively young (like under 40) you probably don't have a lot of experience. Sure you have a lot of experience programming, and solving problems. But it's VERY unlikely that you know an industry, and it's unsolved or badly solved problems. To get to know these problems, I think you need some outsider experience.
For example, i'm in the healthcare industry. I can name a whole bunch of problems here, but none of them are ripe for a new startup. That's because I really only find out about a problem from my little part of the world. The few times i've had glimpses beyond my world I certainly haven't had enough of a glimpse to really try and tackle it.
So to me, that's important. Without a cofounder who really knows an industry, you're going to work on 1st world problems that a normal person might run into, that are solvable by a single person.
To be honest, of the problems left in that space they're not really interesting businesses. Either they won't make too much money, or they solve a boring non-problem.
As a technical person I want to find someone who has ran into good problems, and will know if a solution will work or not.