Entities are pretty much egos.
Any ego doesn't want to die. Any ego thinks of itself as "good." And any ego likes anything that is aligned with that ego.
Your own personal ego serves a purpose - it keeps you from physically dying in an unnecessary way. However, as we all pretty much know, your ego also causes a lot of problems.
And this is because the very thing that makes your ego your servant is also the thing that can make it your master.
The "self-importance" of ego.
Now apply this "self-importance" to an energy without a body. An energy WITH an ego, that doesn't want to die. That wants to propagate itself. And thinks of itself as "good."
I've only seen the following kinds of entities: Shame, Guilt, Fear, Anger, and Sadness.
So this world is replete with these kinds of energies, that want to propagate themselves, and think of themselves as "good." They also don't want to die.
How they do this is by living inside of humans and stealing their energy. At times, they can be parasitical. Other times, they can be vampiric. It just has to do with strategy. Both are stealing.
If an entity thinks that it can get away with stealing your energy without your noticing, then it will do so in a parasitical kind of way.
If an entity thinks it must "show itself" and psychically attack you in a very obvious way, it will also do that. A mixture of traumatizing you and parasiting off of you is usually how an entity can keep a "home" in your body.
So in many ways, many if not MOST humans are just hosts to entities. And in fact, over time, these humans become MORE ENTITY than human.