Well we just make sure its not garbage in, that is all. The human brain is only a finite object, if we simulate enough of it, we reproduce a human personality. You don't need subatomic precision to simulate a human being, you need only cellular precision, if we move an atom out of place in your body, you are still you. Much of the random molecular movements is not really information, those can be simulated statistically through the gas laws for instance. A cellular model of the human brain is a lot less complicated than a molecular or subatomic one where electrons all have to be tracked in their orbital shells, that is definite overkill. The errors in the approximations you make cancel each other out if the simulation is sufficiently precise. One can for instance predict the weather without simulating the path of every molecule and atom in our atmosphere, there are statistical means of tracking air masses and weather fronts. The human brain can be simulated in similar detail. Telepresence is when an actual real human being operates a robot by remote control, if that robot is simulating a human being internally, then its not real telepresence as its not remotely operated but internally operated.