Don't take on so about the universe (she said, winding her shuttle with rapid flicks of her fingers). The universe is tougher than you seem to think. What might look to you like the flimsiest of chances are made up of causal chains as vital as spider's silk, at least as strong as this web of mine. (She ran a thin fingertip across her warp, and it sang softly, like a harp tuned all to one key.) It bends, or bellies out in the wind, but it won't break. And there are no paradoxes.
(She set the shuttle to the web, throwing it swiftly from hand to hand, while the thunder grumbled high overhead. Some, like the Spanish barber, are no more than a trick of the language; others, like the man who murdered his grandfather, put themselves out of existence. The best you'll ever see is some poor little contradiction that looks as if it might grow into a paradox: but it always dies a-borning.
You might have thought there was the making of a paradox the day Peter Bannister fell through the time hole. He fell from the twentieth century A.D. to the fourth century B.C., and landed with a hell of a thump.