If my goal for the day is to run two miles, I feel exhausted by the time I finish. If my goal is to run four miles, I don’t feel exhausted at two.
This reveals to me that it’s all about the mindset. Obviously I’m physically doing the same amount of exercise by the time I finish two, so I believe that the difference is in my expectation.
My brain is constantly looking for an excuse to stop pain. If it is convinced that the pain will not stop at 2 then it’ll do whatever necessary to cope. And it copes by telling itself that this pain is normal. But if it knows I will stop soon, it will stop trying to cope.
Lesson: whatever your goal is, always aim a few notches above it because it’ll give you the mindset of a person who sees the original goal as normal.