Most people are creatures of habit. Once they make a decision ("this is my brand of toothpaste") they tend to stick to that in spite of any new information.
This reminds me of a quote from Surely You're Joking, Mr. Feynmann!.
"When you're young, you have all these things to worry about - should you go there, what about your mother. And you worry, and try to decide, but then something else comes up. It's much easier to just plain decide. Never mind - nothing is going to change your mind. I did that once when I was a student at MIT. I got sick and tired of having to decide what kind of dessert I was going to have at the restaurant, so I decided it would always be chocolate ice cream, and never worried about it again - I had the solution to that problem."
There's one exception to that which is that it's sometime more fortuitous to throw energy into developing something you already know further rather than throwing all existing knowledge away and starting again on a whim.
"When you're young, you have all these things to worry about - should you go there, what about your mother. And you worry, and try to decide, but then something else comes up. It's much easier to just plain decide. Never mind - nothing is going to change your mind. I did that once when I was a student at MIT. I got sick and tired of having to decide what kind of dessert I was going to have at the restaurant, so I decided it would always be chocolate ice cream, and never worried about it again - I had the solution to that problem."