If you think you'd like to say, "Cancel," to a thought in your head...you already are!
Follow that by jumping up, or sitting down, or going to a window, or another room...or indoors, if you are out, or what's for dinner...something to change your focus.
No one will ever know what you thought, not even you, because your marvelous brain is busy 'cancelling' it...and rushing on to the next thought.
Our brains behave like monkeys in a barrel, so we won't miss any possibilities...but they are OUR monkeys, and ours alone. They 'have to' do our bidding...isn't that nice?!