Some people will never believe in something that they haven't seen at the zoo or that can't be somehow arrived at as an answer in a known equation. It's why I long for the day that something like a "mythical" ape or lake monster or sea serpent's body is brought before science... so that I can fall asleep that night knowing that they were all forced to deal with the fact that perhaps they aren't as all knowing as they believe themselves to be.
Or perhaps an encounter with a supernatural being, or occurance that they can't explain, yet know without question happened. Then you hope that they are met with smart ass close minded comments when they try to tell others about their experience. You know, the same types of comments and reactions that they have spent their lives spitting at others who were already aware that such things existing.