There is this detrimental mentality when it comes to fitness that progress should be linear or it is pointless.
I ask you to think about a big change you attempted, such as a "new year's resolution". How often as the goal fallen to the side? Have you noticed that as you get older "giving up" becomes easier to justify?
I have struggled with perfectionism since childhood and only in the last few years have started to practice a new understanding of change. Ask yourself the following:
"Three steps forward with two steps back" often gets a bad reputation but I think its the best way to start toward a goal and maintain progress. Start with a ramp up (learning period), followed by a short uncomfortable challenge (push period), think about what you feel capable of moving forward with (reassessment period), practice the new skill until it becomes habit. Then, the cycle starts again. Consider how we all have mental, and physical, set-points. Our minds and bodies can only maintain so much change when unprepared.
I am not discounting the effectiveness of challenging yourself because that definitely has value. I am challenging the "all or nothing" mentality. Challenge expectations, by definition, are not sustainable.
Human nature prohibits us from constant competition with oneself. No one can be "perfect" at anything. The best we can do is make progress toward a goal. And there is a point, especially with fitness, where additional progress isn't physically possible. Sustaining is also only possible for a finite period of time. We don't blame the car for needing an oil change, why be so tough on your body for hitting a natural limit?
"God grant me the serenity to accept the things I cannot change, courage to change the things I can and the wisdom to know the difference." ~Reinhold Niebuhr (1892–1971)
I have found great value in pushing and then relaxing to enjoy the fruits of my labor. After all, the act of trying is a triumph in itself.