There is the idea of staying in the moment.
Being able to not think about your score or your bad shots. to be able to make the preasure putt, to be able to come back after an opening day bad round to end up wining.
There is the playing with the lead on the final day. Or coming from way behind on the final day to win.
Tiger , Jack, Hogan, to name a few that were famous for their mental toughness in all of these areas.