Going solo is terribly hard. The worst part is that you don't know how much you're missing by not having a co-founder until you've seen what great collaboration is like (spoiler: it is really good).

Of all the great things to get out of doing Y Combinator three years ago, the best by a mile was teaming up with Sascha to work on BaseShield. We ended up shelving that product but it's incredible to look at BaseShield and now Ninite and realize how completely they were shaped and improved by our collaboration.

I'm not talking about the set-theory union of our ideas, it's more like a tug-of-war as we'd shape the concepts and features underlying our work. Ideas always improved through this process, often radically. This was especially true for core questions like what does it do, how does it work, and what will users see.

Briefly, if it seems OK to work alone I'd say it's because you don't know what you're missing.