Fear is the Mind Killer.

A few thoughts by the artist Wassily Kandinsky about the people at the top of science, art, philosophy (and the majority of their followers):

"But despite their patent and well-ordered security, despite their
infallible principles, there lurks in these higher segments a hidden
fear, a nervous trembling, a sense of insecurity. And this is due to
their upbringing. They know that the sages, statesmen and artists
whom today they revere, were yesterday spurned as swindlers
and charlatans. And the higher the segment in the triangle, the
better defined is this fear, this modern sense of insecurity. Here
and there are people with eyes which can see, minds which can
correlate. They say to themselves: 'If the science of the day before
yesterday is rejected by the people of yesterday, and that of
yesterday by us of today, is it not possible that what we call
science now will be rejected by the men of tomorrow?' And the
bravest of them answer, 'It is possible.' "

Closed mindedness is the attempt to ignore the fear that our ideas could be wrong; a coping mechanism. It prevents us from seeking more. Not facing our fear is what truly kills our minds.