In the last 24 years, since Affirmed won the Triple Crown, only two horses who have won the Kentucky Derby have also won the Belmont. Winning the Belmont directly after winning the Preakness has been more common (5 times).
The Triple Crown participants who run in all three of the jewels are doing so in a compact 5 weeks. None is likely to run this often again.
Three year old horses are still developing, which adds a degree of difficulty to predicting their performance. The distance of the race, 1 ½ miles, is further than any of the participants have ever run. For many, this race will mark the only time in their career that they will go that far. Also, despite the great distance, most will be carrying more weight than they ever have (126 lbs). The layout of the Belmont track itself is unique with its long stretch and sweeping turns, perhaps giving certain running styles an advantage.
In the final analysis, of all the attributes a great racehorse may have, this race begs for a horse with stamina. So in finding the next Belmont winner, one can ask the question: “Which horse has the genes, experience, recent form, and the heart to win the Belmont?”
Live Longshots in the 2013 Belmont