I went back to school in my late twenties and obtained a B.S. in physics. Since I already had an established career, this required no small sacrifice. For me, I started out [not knowing this] needing to prove to myself and everyone else that I could do this. In the end though, it was my love for the subject that pushed me through the wee hours of the night. I wanted to understand this stuff and I wasn't going to quit. QED!!!
Reference https://www.physicsforums.com/threads/what-inspires-you-to-learn.6103/