Roger Federer's mental toughness as a young player was scathingly analyzed by Pat Rafter, who remembered how the Swiss maestro wilted against him at the French Open.
Fans mostly remember Federer for being at the top of tennis for several years, taking the sport to a new level with his graceful style, and having epic rivalries with Novak Djokovic and Rafael Nadal.
However, it took Federer a while to go from talented young player to great champion. The eight-time Wimbledon champion has openly admitted to having outbursts on the court and not working as hard as he could have.
Two-time US Open champion Rafter also noticed a lack of mental fortitude when he played Federer as a 17-year-old at the 1999 French Open. It was the eventual tennis legend's Grand Slam main draw debut.
Speaking to the ATP, Rafter described how he responded to losing the opening set by showing energy and getting in Federer's face, something the then teenager did not respond well to.
"Roger Federer came on the scene in ’99, and I got to play him; he got a Wild Card I think. He came on, and he beat me the first set 7-5. I was like, 'You punk!'"
"I was trying to work out how I was going to get through to him as well, and I got off in the second set, and then he might have done a double [fault] or I won a big point and I just got in his face and went 'Come on!' He sort of melted a little bit. He was a little soft at that stage."
Rafter also won his next two matches against Federer in Miami and Halle. The Australian jokingly said he retired as the Swiss started to become the best player in the world to avoid being beaten by him repeatedly.
"You know, once he sorted that part of his game out, oh my god, it was such a good time [for me] to leave the game. He wanted me to stay so he could start beating me, and I was just trying to get out of the game as quickly as I could."
Despite not being as successful, Federer's early years are fascinating to relive now that he is retired. The 43-year-old was much rougher around the edges and was trying to learn how to be the best.
Serena Williams' former coach, Rennae Stubbs, recently compared teenage prodigy Mirra Andreeva to the young Federer. Andreeva, like Federer at the start of his career, is prone to outbursts when things are going badly.
Although this year's Dubai Championships and Indian Wells Open champion may never be as cool on the court as Federer became in later years, she will undoubtedly mature mentally, which should make her even more formidable.
Debates continue about whether Federer, Nadal, or Djokovic is the greatest player ever. Djokovic is the most statistically successful and Patrick Mouratoglou thinks his confidence has made him the best. However, others argue Federer had the more significant impact on tennis.