Ask HN: Working two jobs

I am fortunate in that I have two jobs. I work 3 days a week as a sysadmin and two days a week on my SaaS product. My income works out roughly the same as if I were full time sysadmin.

Having painted a picture I'd be keen to hear from anyone who knows about the mental gymnastics and motivation required to work two jobs? What have you learned and how do you stay on task?