From Steven Moore's taichiheartwork blog
"If you don't have the feeling that the next stage – infinite in its extent and awful in its implications – is forever looming – beckoning and threatening – then you're stuck. This is what gives the great master his indomitable spirit – each day is a ride on the back of the dragon into the fray."
See http://taichiheartwork.blogspot.co.uk for other posts.
This is so true if you are really investigating your T'ai Chi, not just going through some daily motions which are nothing more than superficial performance.