Going at 100% of what you can do means that the next 1% will break you.
That is the maths.
That is what 100% means.
101% is the breakdown number. It is the wall, hit hard.
When I feel myself speed up and I see that wall coming - I wilfully slow down. Just a tad. It is hard.
Life lived at 80% means that I can flex the extra 10% in moments that truly require it and still have a bit over for safety.
Because that wall is always closer than I think.