Such things as vampires to levitating, whether it is possible or not is something you should decide, but decisions should be able to change if the proof or lack of proof is good to you.  Many are too close-minded and just agree that something is impossible.  For example, in the future I may actually regret thinking the way I do now and start being "one of the guys."  While this idea totally disgust me, I know that there is possibility that it can happen.  I can accept this and many other possibilities, but can you accept the many possibilities about yourself or the events of the world?