It's not about fear of failing. I wouldn't do it again unless I was convinced the venture would be successful (and I think there's a significantly increased chance of that, based on what I learnt during the failed startup and since).

What I'm saying is that having equal co-founders gives you the ability to share the workload, emotional strain and get through the pain barrier.

It's obviously not impossible to build a huge business as a single co-founder, but it's unlikely that I'd want to do it again!