The Kentucky Derby is not only a test of speed and stamina – it is a test of mental fortitude for a young horse, with the pressure cooker culminating in the “wall of sound” as the field turns for home in front of more than 160,000 at Churchill Downs. Mendelssohn has shown the speed and stamina, and his breeders think he has the mental fortitude to handle the stress of the May 5 Derby.