Nietzche says "when you look into an abyss, the abyss also looks into you"
My body knows when a jump is near the limits of my ability, I feel it in my legs. I'm still new to Parkour, but I suppose no matter how long you have trained for, a new jump that tests the limits of your ability is something you need to think twice about.
One of the useful things that can be learnt by just watching more experienced people is that they only do things when they know they feel that they are feeling upto it. I remember watching one of the best Traceurs I know spend a considerable amount of time looking at a jump that was well within his capabilities, yet because it was new to him and he didn't feel like doing it there and then, he waited and made the jump successfully first-time on another day when he did feel upto it.
A pilot that has extensive experience flying planes would not jump into the cockpit of a brand new plane that they have never flown before and expect to fly perfectly first time. It would take time to get to know the capabilities and controls, no matter how well you flew your previous planes, stepping outside the limits of your ability is a risk.
Don't disrespect gravity, and it won't disrespect you.