This is from The Last Continent by Terry Pratchett.
"It's not just that things in the future can affect things in the past," he said. "Things that didn't happen but might have happened can...affect things that really happened. Even things that happened and shouldn't have happened and were removed still have, oh, call 'em shadows in time, things left over which interfere with what's going on."
I love sentences that get all twisted up and with some thought makes a lot of uncommon sense. A lot like my I Am What I Am phrase I posted.