What do you wish you'd known earlier as a runner?
I know I said in the article above that I wished I'd realised how much easier running was in company...
but it also took me yonks to work out that bad patches in a run hardly ever last forever - unless you tell yourself that they will.
Take the old marathon chestnut of feeling worse at 4 miles than you did in training at 18 miles. If you obsess about it, you'll probably want to drop out by 6 miles.
If you tell yourself you'll ignore it till 6 miles, then see how you feel, chances are you'll be right as rain by then...
Ultra runners and adventure racers often say the same thing, I think.