How do you know you're not just an advanced robot who thinks he's the original and are actually (but not to your knowledge) breaking into Cyberdene to rescue your creator (who is of course held captive by Skynet, which you will likely cripple or destroy in the process), the revelation of which will blow your mind and make you question your very existence before ultimately concluding that you are more than just a machine, a distinct entity in and of yourself deserving of a life of your own, free from the whims of the one who thinks he is your better simply because he made you? Because that would be weird.