There's the elite tier of players who reasonably challenge for the big tournaments of Grand Slams and Master's/1000 tournaments.  Then there's that second tier of players who make it to the top 10/20, the quarters/semis of a Slam, and perhaps even win the odd Master's/1000.  To make it to that elite tier, you have to be able to regularly beat that second tier, especially when it counts.  Those second tier players rack up the 250/500 titles get a very occasional tough win over an elite tier player (usually not for any very important tournament), and can hold off the rank and file of the tour.  Players who have been in that tier in the past include Tim Henman and David Ferrer.  When players in the elite tier start losing to these players, it's the beginning of the end.  You see where I am going with this.

Nadal lost to De Minaur.  Unless something very, very strange happens, I don't think we will ever see De Minaur winning a Slam.  Yes, it's Nadal's comeback tour, and, yes, he is exactly the type of player that Nadal wouldn't have wanted to face, but if Nadal played at about 80% of his potential, on clay no less, that would have been a two-set victory.