Daniel Kolak’s Open Individualism
Open Individualism is the theory that the boundary between you and other people is a total illusion created by your brain. While we usually think of ourselves as separate streams of consciousness, this idea suggests there's actually only one single observer in the entire universe.
Your memories and your physical body act like a filter that keeps you from feeling everyone else's experiences, but the core *awareness* inside of you, is the exact same awareness inside every other living being. This means that you're essentially a single spark of life playing every role in a massive cosmic story at the same time. When one person dies and another is born, the same *I* simply continues on in a different body with a different set of memories.
Substantially, there's no real distinction between yourself and a stranger because you're both just the same consciousness looking at the world from two different seats.