I think these apply perfectly to breathing (or any contemplative practice):
“Any technique, however worthy and desirable, becomes a disease when the mind is obsessed with it.”
“The individual is of first importance, not the system. Remember that man created method and not that method created man, and do not strain yourself in twisting into someone’s preconceived pattern, which unquestionably would be appropriate for him, but not necessarily for you.”
“The more complicated and restricted the method, the lesser the opportunity for the expression of one’s original sense of freedom.”