Never define yourself by a single workout. Progress comes from consistently working at your best, month-after-month, year-after-year, rising to whatever level you can rise to on any given day. If you pay too much attention to how you feel during a single workout, you will get whiplash from all the ups and downs. Most of my best workouts are preceded by absolute disasters, and vice versa. We're not robots. The ups and downs are part of the process. They're not problems to be solved. Embrace bad days because you get to practice being the type of person you want to be when things are not going well.