Entertaining an idea is understanding it. And, there is some research to show that understanding an idea is believing it. Hence, understanding an idea and not believing it is very effortful.
[1] https://bear.warrington.ufl.edu/brenner/mar7588/Papers/gilbe...
https://archive.org/details/religionpursuito0000lowe/page/n5...
Along the same lines: "Education is the ability to listen to almost anything without losing your temper or your self-confidence." -- Robert Frost
apparently not, actually:
"The earliest that this quotation appears in print is in Religion and the Pursuit of Truth (1959) by Lowell Bennion."
or
"First attributed to Aristotle in Lowell L. Bennion, Religion and the Pursuit of Truth (1959). Unfound as such.
Sometimes thought (though I feel it's a bit of a stretch) a misinterpretation of Nicomachean Ethics 1.3.4 (1094b): "For it is the mark of an educated person to search for the same kind of clarity in each topic to the extent that the nature of the matter accepts it.""