If you believe in something, you will see it, believe me...
I asked a friend of mine to go out to a deserted field at midnight, and just wait half an hour alone there, and see if he could see "it"... Just 10 minutes later, he ran back, stricken, sneezing, cold, and with a horrified look on his face... Yes, he did see "it"...
Another friend; I told him to do the same... And he came back 40 minutes later, hungry, and blasting me for wasting his time...
I've done this experiment a few times already to some of my friends (sometimes it's deserted fields, sometimes it's abandoned houses etc), and ask them what they actually see (or don't see)... It always differs from one person to the next...
My schoolteacher taught me this particular experiment.