Nonlinear Progress
I'd begin every season of serious training with a few very disappointing workouts. "If this pace feels so hard then how the hell am I going to hit my goal in twelve weeks?" Then sure enough, with a little bit of focus and consistency, twelve weeks later I'd surprise myself. Sometimes the disappointment of losing to your own ghost in a workout can motivate you to try harder in the next one, and that's what you need. Most times, though, it's best to take solace-- or even celebrate-- the work you did. The work is all you're entitled to, anyways.