A book that makes you to keep going on no matter what

I lack discipline to do work. I'm almost hitting 30 and still lack discipline in my work. I scrutinize myself a lot on whether I'm really putting in the hours or not, contributing meaningfully or not.

I'm looking for a book that talks about how a person can keep going no matter what — to be like a perpetual machine; working perpetually without any motivation or anything of that sort