Think about how hard it is to make an Olympic team. In order to have a chance at making the team, an athlete has to be elite, always among the best of the best.
It takes years of practice and years of competition to have a chance to make the team, and then it comes down to a performance in an event like the Olympic Trials to determine eligibility.
This is a nearly impossible goal, and few end up making it. They are clearly very special athletes.
Now take it one step further: athletes who make the Olympic team in two different sports.