"But that can't work, can it?" Said Richard. "If we do that, then this won't have happened. Don't we generate all sorts of paradoxes?" Reg stirred himself from thought. "No worse than many that exist already," he said. "If the universe came to an end every time there was some uncertainty about what had happened in it, it would never have got beyond the first picosecond. And many of course don't. It's like a human body, you see. A few cuts and bruises here and there don't hurt it. Not even major surgery if its done properly. Paradoxes are just the scar tissue. Time and space heal themselves up around them and people simply remember a version of events which makes as much sense as they require it to make. That isn't to say if you get involved in a paradox a few things won't strike you as being very odd, but if you've got through life without that already happening to you, then I don't know which universe you've been living in, but it isn't this one"