What does Clinton Anderson say is the single most important thing to do before the first ride on a colt?

Clinton Anderson is unequivocal on this point: the single most important thing before the first ride is groundwork, and specifically groundwork that confirms the handler has complete control of the horse's feet in all four directions — forward, backward, left, and right — from the ground. His position is that every bucking incident he has ever witnessed or experienced during a first ride was the direct result of insufficient groundwork preparation. The horse that bucks is a horse that still has its feet. Anderson's specific pre-ride checklist includes: the horse yields its hindquarters softly from both sides, the horse yields its forequarters softly from both sides, the horse backs readily from halter pressure, the horse moves forward willingly from a tap or rhythmic energy, and the horse has been thoroughly desensitized to the saddle — including a tarp, ropes draped over its body, stirrups flopping, and the girth being tightened. He also requires that the horse has been worked in the round pen to the point where it hooks on to the handler willingly — meaning when the handler changes direction, the horse changes direction and faces in, seeking the human rather than fleeing. Anderson's philosophy is that if you have to spend two weeks on groundwork before the first ride, do it. The first ride on a well-prepared horse is nearly always uneventful. The first ride on an underprepared horse is where accidents happen. He notes that most professional trainers who start many colts have not been bucked off in years, not because colts have changed but because preparation has become thorough and systematic.