How come human psychology and Risk/Money Management comes under same roof? I would agree if you would have said both are inter-related.
There can not be universal rule. Money management is something tightly coupled with "Risk". And again Risk is subjective and relative. That is why we are having this thread. Earning 2K on daily basis is not same thing for every trader.
Trading systems, indicators you use, management you enforce all are to make you to feel that you are trading professionally. And when you find all these things happen with no much effort on your side, then you have become what you want to.
In first place, what you don't follow your own Risk management rule? You call it not having self-discipline. Then discipline itself is a psychological trait. One could learn to be disciplined and the other may find it difficult. If you say, all are here, are exceptional in this respect, then you are right.
And.. as you said, if one could trade that simple by following the 3Ms easily, believe me trading would be the most popular profession on the planet.