Solo technical founders, has not having a business cofounder even screwed you up? "I will not promote"

I’m creating an AI startup; a reinforcement learning model designed to do a certain thing in a big field.

I’ve basically developed code for a prototype (I hope to start training in two weeks)

I do believe YC advice for taking a cofounder, but risk of getting a bad one is too high. In my life I also haven't met people with my grit, at least from my countries, so I'll have to "date down", I guess. At least in technical sense.

So, has not having a business cofounder actually screwed anyone up badly? 

(Looking at people who are doing ventures with $20m+ potential/real ARR,)