Group
Probably what you know and opine has been influenced in a strong way by the information and opinions of the people you have met and talked with.
Strong attachment with the group of people around us makes us unconsciously agree with the same opinions and ideas as the group.
And when those people around have some shared view, the view inevitably becomes our view.
This leads to irrational thinking and narrowminded views.
What is required is the ability to independently reason for oneself, taking the opinions/data from the group into consideration.
The countries that were out of the scene when reason and science were being invented routinely fall victim of this .... though how are these two facts related is less obvious.