What do we really mean when we talk about ourselves, our self? Is there really such a thing? Or is who we are a variable that changes with time and situation?
At the heart of our conceptualisation of the self is this notion of identity, meaning one, meaning a stable and consistent set of values, beliefs and preferences that define who we are - in other words, a personality. But how true is this conceptualisation? And even if it is generally applicable, does it need to be? Anecdotally, we know that there are people who behave very differently in different contexts, so that we find ourselves saying things like "Oh, he / she was a completely different person then". It is possible to possess multiple identities, multiple selves?
Understand, I don't mean this in the involuntary, schizophrenic sense. I mean, rather, can we choose to adopt different identities, can we choose to be different things with different people, in different settings? Understand also, that I'm not talking about a multiplicity of identities that comes from pretense  - most of us, at some time or the other, have pretended to be someone we're not. What I'm talking about is the act of authentically experiencing different identities as being true, of genuinely relating to these different persona as all being the 'real' you.
Is this possible? I believe it is. I think it is possible to find stimulation and satisfaction in a wide variety of different (and sometimes opposed) life experiences, and in some cases the only way to explore those experiences fully may be to construct (and live) different selves for each. Say, for instance, you're really interested in physics and poetry. As a physicist, you'd need to be logical, fact-based, analytical. As a poet, you'd need to be creative, impulsive, unstructured. My contention is that you could do both - that you could live your life in a way where those who worked with you as a physicist found you structured and precise, and those who watched you write knew you as someone who was chaotic and wilful. (Whether you'd be really good at either is a different matter, and one that need not concern us here).
How can this work, you ask? What does it mean to have preferences and 'values' that are so variable? First, I think that different personal attributes have different salience depending on context. So, for instance, you may be deeply religious at home (I'm not, but just by way of example) but not consider religion to be an important component of work place interaction. So actions that you might be opposed to at home may be perfectly acceptable to you in the workplace. In an Indian context, the classic example of this is people who eat non-vegetarian food outside but don't eat it at home. For these people, there is no contradiction in such behaviour, because for them, home is a very different environment from outside.
That said, I do think it is true that maintaining fundamentally different selves requires a certain degree of control over one's emotions / preferences. Or, alternatively, it requires the ability to switch between selves, to throw oneself whole-heartedly into a new personality so that it doesn't just feel real, it is real. In some sense, this is the creed of the good actor taken to an extreme. Whether this is truly possible is, unfortunately, a question that cannot be emprically answered (how would you ever seperate what was pretense from what was real) but personally I think it can be done. More, I think it's one of the most exciting and fulfilling ways to live your life. To the extent that we have only one life to live, adopting a multiplicity of selves may well be the only (though admittedly imperfect) way to try out a number of different conceptualisations of who we could be.
 From a purely existential perspective, of course, it's not clear that there's any real distinction between the two - to be something is to pretend to be it, only with absolute conviction.