Rafael Nadal recently held a public interview, discussing Novak Djokovic and how their careers unfolded among other things.
Nobody really expected Rafael Nadal to have the career he had when he started to play tennis. You could say the same thing for Djokovic, but it's even more true for the Serbian. Both careers were incredible and surprising to many, despite the undeniable talent of both ATP stars.
You only needed a small sample size to understand that both are far better than your average tennis player at a young age, but even they didn't believe that they would be sitting at 20+ Grand Slams one day.
Djokovic leads in that regard, having won the 24th Grand Slam recently in New York while Nadal is still at 22, which came at Roland Garros last year. He spoke a bit about the Grand Slam race in his most recent appearance on Movistar+, explaining why Djokovic had more Grand Slams than he does.
I've missed four and a half years of Grand Slam in my career, but that's not why I'm better than Djokovic. He has been better because he has a physique that has allowed him to play more than me. Maybe I'll come back and win three more Grand Slams, although it's unlikely.
Nadal is right that Djokovic was a bit more lucky with injuries, though you can debate whether that stems from luck alone or whether the Serbian's dedication helped him preserve his body better. Either way, he had fewer injuries and played more, which matters.
Even now, the Serbian looks in a better position. He finished the year with three Grand Slams, while Nadal didn't play due to injuries. Nadal is older, but he's not that much older, not even a full year, so we can see the effects of their health impact the careers of each one in real time.