That physical damage to the brain results in loss or impairment of consciousness, and that there is absolutely no evidence that total biological death would entail anything but the cessation of this consciousness.
[EDIT: I want to be clear - I am NOT saying that it could never be the case that some form of "being" exists outside of what appears to us as a finite biological existence, I am merely pointing out that we have no evidence of this kind of existence, aside from vague spiritual feelings and experiences which are difficult to evaluate, so the skeptical position is the most honest one for the time being.]
[EDIT: I want to be clear - I am NOT saying that it could never be the case that some form of "being" exists outside of what appears to us as a finite biological existence, I am merely pointing out that we have no evidence of this kind of existence, aside from vague spiritual feelings and experiences which are difficult to evaluate, so the skeptical position is the most honest one for the time being.]