Yea..... Sampras was just going or the record. And he didn't try hard in all of them. He basically quit the French after '96 ( As his blood disorder caused him fatigue) so he focused primarily on the Wimbledon/USO.
His goal was 13. If the Goal was 20 he would have surpassed that to if he put his mind to it.
Its all about having a Goal number in front of you and something to shoot for
yeah, like federer aiming for 19 because the all time record before that was 18 (which he owned)
and when he had 17 he aimed for 18 (which he owned)
and when he had 16 he aimed for 17 (which he owned)
and when he had 15 he was the undisputed GOAT.
he keeps aiming to beat his own records (not sure if you've noticed, but sampras doesn't really have any that federer hasn't already beaten FYI), which is like you said. it's always good to have a number in front of you. sampras needed to beat others, federer needs to beat his own since he beat everyone else's back in 2009.