A lot hinges on the fact that, in most circumstances, people are not allowed to hit you with a mallet. They put up all kinds of visible and invisible signs that say, 'Do not do this' in the hope that it'll work, but if it doesn't, then they shrug, because there is, really, no real mallet at all.
Terry PratchettWHAT WOULD HAVE HAPPENED IF YOU HADN'T SAVED HIM? "Yes! The sun would have risen just the same, yes?" NO "Oh, come on. You can't expect me to believe that. It's an astronomical fact." THE SUN WOULD NOT HAVE RISEN. ... "Really? Then what would have happened, pray?" A MERE BALL OF FLAMING GAS WOULD HAVE ILLUMINATED THE WORLD.
Terry PratchettWhatever you choose, your choice will mean there are two new worlds. And perhaps sometimes, on the edge of sleep, we will see the shadow of the other world. There will be no unhappy memories.
Terry Pratchett