Personally, not knowing where I might end up is scary. I like to have a grasp and firm control on things... I don't like not knowing.

I don't know and that terrifies me

Part is the idea of failure or messing up so bad there is no going back

They don't like to suffer, they don't enjoy discomfort and very few people truly like pain. And doing something open ended when you are uncertain of the outcome could cause any one of those things.