Can we know whether anybody else exists? Are we the only conscious being that exists? Is everything else a projection? Some say so. Solipsism is the belief that everything external to our mind is unsure, and that it is impossible to know whether anything outside ourselves is real.
Gorgias the Sophist was the first philosopher to entertain solipsism and scepticism, and Descartes, in his meditations, wrote that we can only know that we ourselves exist. Solipsism can lead to depersonalization disorders and indifference to the world-if it doesn’t exist, why care for it? However, a solipsistic world view is bound to crumble when surrounded with other people, otherwise permanent detachment, and maybe even madness, will ensue.
Philosophical Fragments 
A favorite one-liner: “Is it solipsistic in here, or is it just me?”
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Perhaps solipsism is an unfortunate evolutionary development of extreme self-centeredness, common among narcissists and in more extreme cases, psychopaths. The recognition of ‘the self’, or to be more precise ‘the me self’, may be a neurological mutation that began to develop in Homo sapiens in Palaeolithic times and has increasingly intruded on ‘the I self’ (to use William James’s categories) ever since. It appears to be an a conceptually-conscious a priori process of trying to understand reality objectively, as distinct from a sensually-conscious a posteriori process of experiencing reality subjectively, with disastrous long-term consequences for our species future survival. I amplify this idea in: ‘The Rise of the Mutant Ego’.
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