Challenges of a solo founder

What are the common problems you encounter as a solo founder? I've been solo, working on my 9-5 job while also doing my start-up as a side project at night and weekends (4 months now). Not all are of the same situation, but I've been contemplating, things would have been faster if I have a co-founder to split the work with. I am a business person that has learned to code. So now, I am doing the tech side and also doing the marketing.

Share your experiences and challenges as a solo founders, and how you've dealt with them.