Beyond mental toughness and genetics is want.
Ive stated on here before that i have no want at all to do an Ironman and tere were some who understood and some who said "that i protest to much".
I love triathlons,I love watching Ironman, but I cant imagine wanting to do one. Its just not something that interests me.
Do i have the "genetics" probably,I think if i trained i could do a Ironman in 12 hours or there abouts,do I have the "mental toughness" yep,ive never not achieved something ive wanted to do.
Its the "want" thats missing.