Rules and discipline are different. Discipline is an outlook, a program, a way of organising the world as it impinges in a headlong rush upon oneself. Years ago I had to spend three months in hospital. On the second day it dawned very clearly I'd need routines to survive the boredom of the place. At every moment of the day I would have to have something to do, read, listen to, whatever. I needed a timetable. I see discipline not as time management but as time allocation. Another bit of your brain decides what you like doing, what you think you should do, and discipline is allocating the right amount of time. It's no good being heroic. I now write in two hour bursts. Before I would set aside an entire day - so inevitably there was a lot of wastage. So much so it really became a drag to even contemplate writing. One hour is not enough to get away from the sense of time pressure, three hours is too much for me- I'll start malingering- but two hours works.
Zen monks have a rigid timetable- every minute is accounted for. BUT they are allowed to break it anytime if someone needs their help or if some emergency impinges. The point is, they are never asking themselves 'er what shall I do now?'
The people I know who get the most done and seem happiest about it, allocate time well. They know themselves. The richest 'achiever' I know told me he needs 9 hours sleep. No five hour heroism for him. But when he's up he's running.
Time allocation takes into account wisdom we have accumulated about ourselves and the world over our lives. It is a balancing of right and left brain knowledge. The word 'discipline' is the sharp edge you need to keep up to the mark and not get distracted from your allocated time slots.
And though discipline is often linked to rules there are different. Rules are an attempt to simplify the world. Though they have a role, they inevitably distort the world because of this simplification.
When we impose rules upon ourself and others it doesn't seem quite right. It's like a kind of failure to be alive. O Sensei, founder of Aikido, set up his first dojo and announced there were no rules. Then something went missing from the changing rooms. So he posted the only rule: No Stealing. The nagging, rather self important part of the brain- the accusing self- tells us we must do this and we must do that. Eventually we grow tired of this nagging and throw off all restraint. Maybe later to regret it. And be doubly self-berated for our failure. Discipline heralds from a different place. Whereas a rule is a kind of ad hoc thing, discipline is a world view, an honouring of your own time, the time you have at your disposal. It is an acknowledgement that you can only do so much. It is a break on fantasy and vague wishfulfillment.