Now probably you are wondering about the title of this post, but this is true. We are born into this world as separate beings, having conflicts or a variety of emotions towards other "separate" selves. By doing this, we end up suffering and accumulating karma, which in turn haunts us throughout our lives. We feel bad sometimes out of the blue without acknowledging the root of the problem.
To make the long speech short, we are not our separate selves, a lot of spiritualists and teachers already discuss the dilemma of the self. If you accept that you are part of the whole, if you accept that you are not separate from the universe, if you accept that you are just a single drop of an ocean, then there you are, we are all one.