Last night. Home from work, feeling very tired. Need to do a hard session. Legs still from the day before. Very easy just to say no...
...and then you don't. So, you head out, and after you have passed the 'terrible tens' moment, and stretched a bit, well, maybe it isn't so bad...
...and then you pick it up and hit the tough work. 5 x 1 mile at pace..first mile ok..maybe we can do this?
..then mile 3 comes and that's a push but you do it..
..and then you find the second wind
..and before you know it, it's over and you can bask in the glory of having cracked it!
Not sure it helps understand how or why!