Everyone asked what is the most advanced movement, and most would tell you that piaffe, the trot in place, is the most advanced of them all.  And the FEI would agree.

But that isn't true.  Because it turns out that piaffe like all the other movements before it as per the Golden Thread is a preparation.  Prepares us so that we find something waiting for us.  And the answer waiting for us is straightness. Preparing us for straightness and the movements that comes from that afterwards.