perhaps i can help grakelin a bit here...
-everything that goes on inside your body to make you who you are, including your sentience is based upon a massive amount of simple reactions. Mostly Chemical and electrical.
-Chemical and electrical reactions can be calculated by a processor.
-Once all of the chemical and electrical reactions that are occurring inside a brain are identified, they can be emulated by a processor.
-In the idea space of this emulation all of the atoms of a body and brain are emulated, and interact with each other in the same manner as they do in reality.
-As this is an exact copy of a mind all of the reactions going on inside this emulated brain carry the same result within the idea space as a real brain does in reality.
on a side note everything you do has a biological motivation, humans are social animals, and have a ton of instincts that drive them to be so, such as enjoying the company of other humans that won't bear your children, as you are now hunting and working in a pack, and more successful in keeping yourself and your children alive long enough to reproduce. I'm always a little surprised when people don't realize how all their actions are based around the furthering of genetic material as similar as possible to one's-self.