Lets take one case study or an hypothetical scenario to clarify the 80/20 rule more better. Stay with me in it.
In the above picture, there is one male (M) and 5 females A,B,C,D,E. Obviously, its one of the social theory that there is a mutual attraction between the male and female, and that in this group the possible outcome would be a pair. All depends upon the M.
Lets assume a scenario that among 5 girls, A loves the M more than anyone. Now, what should M do.
If he is dump and doesn't know 80/20 rule:
He will try to bring a balance in his relationship by committing to everyone equally. He doesn't want to lose any one of them so tries very hard to bring equality in the group. This obviously is not going to entertain the girl A, thus A starts losing interest. Ultimately, there is very likely chance that he won't be able to be close to anyone and then finally, the group breaks and the girls disband him. I consider that a loss.
If he knows the significance of 80/20 rule:
He will focus on the girl A more and gives his 100% to her. In the mean time, he keeps in touch with the others but doesn't try to impress others much. As a result, others respect his feeling towards girl A, and girl A is more then happy to have him.
I consider it a success. Ultimately, he is very happy to have her too. And it makes lots of sense.
And this is actually in more harmony then in the case before.
Harmony always doesn't mean equality, its more then that. If a Business tries to bring equality in the case like above then it is going towards the pitfall. But if it tries the second, then it will bring lots of respect from the customer as well as from those customer that really do not bring any business. So, this is the key point that I wanted to make.