One of the more popular plot lines in science fiction involves the hero going back in time, and preventing something from happening so that in the future they came from some, even more terrible, thing will not happen. For some reason, probably one best explored while watching the currents created by the ice melting in a glass of scotch, the even more terrible thing very often is the birth of some individual. The argument goes something like this: the world, as we know it, is crap. The reason it is crap can be traced directly back to this exact person. Therefore, if that exact person is never born then, ipso facto, the world will not be crap.
