Injury: Focus on What You CAN Do.
Expecting, forcing your body to perform identically during every workout is unrealistic, a recipe for injury.
Energy levels naturally fluctuate. There will be times when your energy level feels lower than on a previous day: modify your workout accordingly. Lift lighter weights. Work either your upper body or lower body. Run a little slower. For now, walking may be your better choice. Modifying your workout is not the same as quitting or giving in.
Take the ego out of your exercise experience. There likely will come a time when you’re injured: focus on what you CAN do. For example, if you’re dealing with a hand injury then concentrate on a more thorough lower body workout. You could use lighter weights but do a higher number of repetitions.
Stay in the exercise game for the long haul. You are in the drivers seat- and there’s no room for your ego.