Why does Clinton Anderson say groundwork is the foundation of everything else in horse training?

Clinton Anderson's position that groundwork is the foundation of everything else in horse training is not rhetorical — it is a functional description of how the specific communication, obedience, and respect established on the ground transfer directly to the same qualities under saddle. His reasoning is grounded in the mechanics of how horses learn and how control of a horse's feet on the ground becomes control of a horse's feet under saddle. Every time a horse yields its hindquarters from the handler's pressure on the ground, it is practicing the response to the leg aid that will displace the hindquarters under saddle. Every time it backs from halter pressure, it is practicing the response to rein pressure that will produce a rein-back under saddle. Every time it moves forward from a tap, it is practicing response to the driving aid. The movements are identical — only the handler's position changes. Anderson specifically teaches that the amount of respect and responsiveness a horse shows on the ground is the ceiling of what it will show under saddle. A horse that will not yield softly to halter pressure will not yield softly to rein pressure. A horse that rushes and ignores direction on the lunge will rush and ignore direction under saddle. This means that every deficiency visible on the ground is a preview of a problem that will appear under saddle, and that the solution to most under-saddle problems is to return to the ground and fix the foundational response. This principle has a practical management implication that Anderson teaches explicitly: if a horse is having a bad day under saddle, get off and do groundwork. Reestablish the responses on the ground, then return to the saddle. He has documented this approach resolving in a single session what days of on-horseback correction could not, because the groundwork addresses the communication deficit directly rather than fighting its symptoms from on top.