And then there is age. Everything just seems harder, or impossible...
No way I'd be doing Escarpment at any pace, so good for you.
Yes, I've noticed that, too. The words "I can't" cross my mind more frequently when faced with a tough physical challenge, i.e., steep hill while running.
Before I get to "I can't" I generally stop myself with "I shouldn't". Fortunately there is less and less temptation to run, now that my walking and running paces are converging.