The origin of the world and what happens after death are distant facts difficult to ascertain, but what about the self? I am a person, you are a person, there are persons all around us, so surely it must be easy to know what is a person. You may say, "Who cares? I know I exist because I eat, I sleep, I make love, I can function perfectly well without knowing exactly what I am, just like a dog."
You probably would not have added, "just like a dog." I put that in to emphasize that such an attitude is no different to that of animals who pursue pleasure and avoid pain regardless of what they are as individuals. Further, do we really function perfectly well? Humans, not to mention dogs, are not so clever at finding and maintaining the pleasure they seek, nor at avoiding the pain they fear, and this is where Buddhism steps in to point out that confusion and misconception about our self-identity is the very source of our problems and our difficulties in finding happiness. It is essential that we find out what we are and remove our misconceptions, otherwise we will go on forever pushing away happiness and attracting suffering in our lives.
Self-consciousness - awareness of self - is innate in all beings, animals included, but what we think we are, our self-image, does not accord with reality. Unaware of how we actually exist as persons, our minds fabricate a mistaken self-image which appears to be real and we live our lives as if it were true. If we mistakenly think our maid has stolen our watch, in our mind she appears as a thief, we even see her innocent behaviour as the guile of a thief, and we angrily accuse and dismiss her. Just as our behaviour and emotions are adversely affected by clinging to the misconception of the maid as a thief, our behaviour and emotions in life are adversely affected by believing to be true the many qualities that we mistakenly project as our own self-image.
The basic mistake in our self-image is that we think our self is something that stands alone, independent of everything else. We think there is a real, concrete, findable ME existing right here on our body and mind and we become acutely sensitive, reacting with hostility towards anything that causes us pain or diminishes our self-image, and with longing desire for anything that gives us pleasure or enhances our self-image. Hostility, desire, and their cause, the mistaken self-image, are the three fundamental disturbances to our mind and its creation - our personal world.
The self that we think we are is a figment of our imagination; so what is the self that does exist? The self that eats, sleeps, and makes love is a mere convention established by the thought "I" directed towards our body and mind. The self has no existence from its own side, and neither the combination of our body and mind nor the label "I" is the self. The self exists, yet it is a mere convention because it can never be located anywhere, and the same can be said for everything else in the entire universe: the earth is a mere convention, your lover is a mere convention, a Buddha is a mere convention, nothing exists in its own right. Everything merely exists in dependence upon a name applied to a suitable basis for that name.
Even though you and I are mere conventions, we still exist and we are able to function as individuals because we have different bodies and minds. Giving a name to our body and mind is sufficient to establish our existence; the self is merely labelled upon the body and mind, there is nothing else. The problem is that, in our ignorance, we think we are something more substantial, and we cling to this phantom with pride, feed it with desire and greed, protect it with hostility, jealousy, and spitefulness, sink into the mire of paranoia or float in a bubble of megalomania, always obsessed with ME, ME, ME!
then can our minds be free of hostility and desire, and be at peace. Just as a mother soothes a crying child who has awoken from a bad dream, the wisdom understanding our ultimate nature - emptiness of existing as independent entities - soothes our disturbing emotions of anger, attachment, pride, and so on, and enables unhindered practice of the source of all happiness, loving kindness.