Kafelnikov had every aspect of the game that a player would need to succeed, except heart. I have watched Yvegeny tank many matches over the years, which proved that he had no heart when his game was off. Great players and great champions find ways to win when they don't have their best stuff. Kafelnikov just found ways to get to the airport quicker when things weren't going his way.
Yvegeny vastly underachieved in his career because he was more concerned with money, rather than grand slam titles. He played week in and week out, both singles and doubles, instead of choosing a sensible schedule that would allow him to be at his best for the slams. Kafelnikov felt that he would always come in second to Sampras, and often asked Pete when he was going to retire, so that he could be number one. Yvegeny should have trained harder, gotten more fit, and developed a sense of pride and passion to improve and take the top spot. That kind of motivation and desire to be the best was always missing with Kafelnikov. Also, I find it strange that Kafelnikov left the game so quickly after his name came up in an online gambling scandal. It makes me question his involvement with that whole scene.
Unfortunately, injury was a huge factor that contributed to the limited success of Richard Kraijeck. Richard was a great serve and volley player, and he was absolutely on fire when he won Wimbledon in 1996. On a side note, Richard beat Pete in the quarters of that Wimbledon, not the semis. I have no doubt that Richard would have achieved more in the game if his body would have allowed it. I don't think Richard had one full year free on injuries in his entire career. He repeatedly had to start over after being away from the tour for extended periods of time.