1001 little things I think.
I remember one of my then fastest red loops at the local trail centre. It’s going back a lot of years now but was single and responsibility free, not very happy with the world (mid-divorce, all sort of other nonsense going on in my head) and I went at it like a charging bull. Somehow my sheer bloody mindedness and diminished sense of any kind of self-preservation meant I rode it in a way and at a speed that I’d never managed before.
Trying to replicate it the following weekend with my more assertive line choice and aggressive braking resulted in me going AOT at high speed, whacking my head, knee and shoulder quite badly. After I’d recovered I cheered up and got slower…
Less dramatically I think being well rested, the bike being right and being in the right good (or bad!) frame of mind can make a big difference.