"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 it's 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 that 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."
    "Well, if that's the case," said Richard, "why were you so fierce about not doing anything to save the dodo?"
    Reg sighed. "You don't understand at all. The dodo wouldn't have died if I hadn't worked so hard to save the coelacanth."
    "The coelacanth? The prehistoric fish? But how could one possibly affect the other?"
    "Ah. Now there you're asking. The complexities of cause and effect defy analysis. Not only is the continuum like a human body, it is also very like a piece of badly put up wallpaper. Push down a bubble somewhere, another one pops up somewhere else. There are no more dodos because of my interference. In the end I imposed the rule on myself because I simply couldn't bear it any more. The only thing that really gets hurt when you try and change time is yourself."