Selfish behaviour is an escalation of the natural wish for resources. Such escalation can cause unwanted conflict and isolation.
Many of our relational triggers can be tracked back to three basic needs we have.
To feel secure in our relationships, we have to manage our biology, our inner idea of what a good relationship looks like, and our relationship with ourselves.
Emotional blackmail attempts to control a person by leveraging their caring reputation. Standing up to it requires firmness.
Being authentic requires skill. We are like carpenters. Our inner values and feelings are our raw materials, but we need to use the tools of wisdom to produce the useful furniture of our behaviour.
We all get taken advantage of from time to time. Those doing it rely either on power differentials, or a degree of hiddenness in their actions. Fortunately, there are things we can do to correct the balance.