In the most physical things you have to fix a programme in order to deal with them, otherwise all becomes a sea of confusion and haphazard. Fixed rules have also to be made for the management of material things so long as people are not sufficiently developed to deal with them in the right way without rules. But in matters of the inner development and the sadhana it is impossible to map out a plan fixed in every detail and say, “Every time you shall stop here, there, in this way, on that line and no other.” Things would become so tied up and rigid that nothing could be done; there could be no true and effective movement.
Ref : Letters on Yoga Vol. II