Roger Federer's semi-final loss at the Australian Open is a real stumbling block for the Swiss player.
Since the American summer, Federer has demonstrated a renewed ambition and stronger wish and determination.
Physically, for the first time in a while, his back issues seem to be solved, and he had finally rediscovered his great movement on the court. His 2010 indoor season was a chance for him to show just how ready he was again to commit to the sport.
By playing further forward, by taking his chances during the points, he also sent a clear message that he was trying to find solutions with which to beat Rafael Nadal in Grand Slam finals.
But in the semi-finals in Melbourne, he fell to Novak Djokovic.
The Serb proved that people will now have to count him as a major challenger and he exposed Roger Federer's limits on the day.
Djokovic found two particular weaknesses.
Roger can no longer play like he used to, beating opponents without caring to consider their strengths and flaws. His margin is no longer the same. He needs to adjust now if he wants to add more majors to his already outstanding career.
Setting up a gameplan and accepting that his rivals have what it takes to make him struggle is mandatory - even more so in the latter stages of a Grand Slam.
He's now having issues with maintaining intensity throughout a match and we often see him relaxing when ahead. During the big matches, when his margin is smaller, those bad habits are coming back to hurt him.
He has to think about how to solve that; maybe through reorganising training. If he manages to evolve again, like he always has done before, he can win more major titles.
But if he's not evolving, his rivals, who are getting better and better, could end his glorious career.