The running of the 133rd Belmont Stakes today evokes mixed emotions in many. While this year's race promises to be a thriller, pitting Monarchos, the Kentucky Derby winner, against Point Given, the Preakness winner, a Triple Crown is not on the line. Racing fans are frustrated, a sentiment that has become an annual refrain. No horse has claimed the crown in 23 years. Are contemporary horses simply not up to the test?

Historically, horses haven't found it much easier; each of the Triple Crown races is more than 125 years old, yet only 11 horses have managed to capture all three. But after so many failures, some fans wonder if Affirmed, who won the title in 1978, was the final one.

There are myriad reasons why Triple Crown winners emerge so seldom. Trainer error can be disastrous; the rags-to-riches hero, Seabiscuit, whose smashing performances made him a national icon, never made it to any of the 1936 Triple Crown races because his first trainer badly mismanaged him. Jockeys are also critical, making split-second tactical decisions while catapulting through an enormous field of horses at 40 miles an hour. Many deserving horses have lost when their jockeys misjudged the pace and gunned them into suicidal speed duels, moved too early or too late, or steered them into traffic jams. Other horses have been foiled by injury.

But it is the challenge of the event itself that fells most horses.

The Triple Crown is an ingeniously conceived test, probably the most formidable in sport, taking the fullest possible measure of every horse. In three races over three distances at three very different tracks over only five weeks, contenders must reach for their deepest reserves of strength, stamina, versatility, durability and consistency. Courage, too, is at a premium, demonstrated most dramatically in 1937 when War Admiral, unbeknownst to his jockey, sheared off the rear of his hoof while leaving the Belmont starting gate, but won the race and the Triple Crown anyway, setting an American speed record.