Selfishness is based on a very strong power of discriminating self with the whole world. I always think in terms of me and distinguish myself from others and I am called selfish. Out of selfishness I always try to benefit myself and don't care about others.
Now imagine that I really discipline myself in attaining more selfishness. I become so selfish that I just indulge in myself and forget everything. The more selfish I become the more I forget others. A time would come when I loose that discriminating power just because it is all about me. I see myself everywhere, everything would be me and I would be everything!
Is it possible that there comes a time when it is all me and nothing else? Isn't it the ultimate realization as per non-dualistic Vedanta?