"...acquisition of new skills never proceeds in a straight line. Progress is more like movements along a spiral, which sometimes advances toward and sometimes recedes from the goal while oscillating upward until mastery is achieved...both [success and failure] are a part of the upward progression leading to mastery" (p. 86).
What a wonderful way of putting it! This is another way of describing what I have said to be good days, bad days, good days, bad days...it continues on until good days are the norm and bad days are exceptions, and then bad days are so uncommon you don't stress over them anymore. The spiral description gives something visual for those visual learners out there.