Always Happy, Or Always Depressed, Same Cause For Narcissists

Narcissists are usually either always happy, or always unhappy and depressed.
The reason is basically because Narcissists are happy ONLY when they're getting the SUPPLY that they want.

So if Narcissist A's SUPPLY is easy for them to get for whatever reason, they're a "HAPPY PERSON".
If Narcissist B's SUPPLY is hard for them to get, then they're going to be moody and depressed.

Let's say both Narc. A and Narc. B's SUPPLY is sexual attention and praise from other people (You're so're so beautiful... Hi there gorgeous...Wow who's that...I'd like to take you home...Hello there...) etc., etc.~

Narc. A retains their looks over the years, keeps looking young and attractive, and keeps receiving positive attention and praise from others.

Narc. B suffers some kind of health problem or injury and along with age, loses their once "gorgeous" looks, and therefore no longer receives the steady stream of positive attention and praise.

Narc. A is getting the supply, and is therefore "Happy".

Narc. B is not getting the very same supply, and is therefore "Depressed".

Nothing else in their lives matters. They won't care about other people whether they're HAPPY or DEPRESSED, although those who are DEPRESSED will often try to hang on to anyone who does give them praise, but that's not the same as "caring" about them, they just found a potential Supplier in a well that's apparently dry.
Those who are always HAPPY will simply discard, reject, or hurt whoever is not giving them enough Supply, including their own kin, and look for someone else to give it to them.

In societies that have a high amount of Narcissism, many people WILL  often treat those who they find physically attractive with positive attention, and will treat those who they DON'T find physically attractive like crap. They'll also treat those they envy (because they're "good-looking") like crap. So the destructive social dynamic becomes a "real" thing, albeit created by the very "thing" itself, spurring more and more people to seek positive attention via their appearance, and buying into the destructive cycle.