"No one tests the depth of a river with two feet." - African proverb
When you read this you say to yourself, duh. Of course not. But this is what so many people do with their belief systems. They adopt a belief system based on one experience, or one incident. Then they prove whether or not that belief is true by jumping into the river with both feet.
They hold onto their belief systems and test them with both feet. Whether or not the belief system serves them and getting what they want.
What belief systems do you have that may very well be true (or not) but do not serve you to believe them because they get in the way of what you want?