Harem members may or may not know about each other. It often comes as a great surprise to most women that the man they’ve been obsessing over, has actually been bouncing around from woman to woman.
Narcissists like secrecy, because if his harem members ever compared notes, the web of lies that they’ve been weaving would come crashing down and he would lose his stash of supply.
He builds up a tolerance to people and the Narcissistic supply that he extracts from them.
Hoarders are afraid to throw anything away in case they have a use for it somewhere down the road.
At worst it shows a user mentality and someone that likes to keep his options open.