There are two main assumptions, going in.

1) people are basically shit, some are just better at hiding it.

OR

2) people are basically good, some are just worse at showing it.

If you only look outwards, each experience with people is seen as proof of one of the above two hypotheses. Thus, you constantly flit back and forth between them; getting overly optimistic, then crashing into pessimism. Or in some cases, you get stuck in one of them; becoming existentially depressed or disgustingly happy. It is only when you look inward that you find out it’s not one or the other. It’s both.