People hang on tightly to our shared mythology--even very intelligent people. Letting go is frightening because it requires a reshaping of our interpretation of reality.
I'd like to present my Theory of Dinosaurism:
One becomes a dinosaur when their hard-wired brain no longer sees it as possible for the status quo to ever *really* change.
When Einstein published his theory of relativity as a young man, it was met with doubt and criticism by his seniors. But it wasnt that these more experienced physicists eventually came to realize that he was right. No, these older physicists died off leaving behind the younger generation that was less blind to the truth.
Einstein became a dinosaur too in his old age, doubting modern theories in quantum mechanics.
We all eventually become dinosaurs, as the leadership in thought falls upon the younger generation who continue to fight for truth and progress.