Our tendencies to get fixated on one thing. Both Royal and I can have a single-minded focus on something and not consider anything else. A small problem with picking up the left lead? I am going to fix it NOW dammit! And I won't do anything until that problem is "fixed" by which I mean it gets slightly better after Royal and I get reduced to sweaty panting messes. Likewise, if something is worrying Royal, he will not stop focusing on it. I once spent an hour trying to get him to stop freaking out about a corner of the arena that a mouse skittered through when we were walking by. Once he decides something is scary or interesting or both, it's hard to redirect his attention. Even though he may be doing what I ask, he's not really "with me".
I think he feels the same way about me sometimes. "I'm getting so sick of cantering to the left. Why can't we do something else?" I like to think I'm improving and getting a better feel for when to quit, but it's been a while since our last "real" session. Only time will tell.