"[There is a] dangerous little catch phrase which advises you to keep an 'open mind.' This is a very ambiguous term—as demonstrated by a man who once accused a famous politician of having 'a wide open mind.'Ayn Rand, Philosophy, Who Needs It
That term is an anti-concept: it is usually taken to mean an objective, unbiased approach to ideas, but it is used as a call for perpetual skepticism, for holding no firm convictions and granting plausibility to anything.
A 'closed mind' is usually taken to mean the attitude of a man impervious to ideas, arguments, facts and logic, who clings stubbornly to some mixture of unwarranted assumptions, fashionable catch phrases, tribal prejudices—and emotions.
But this is not a 'closed' mind, it is a passive one. It is a mind that has dispensed with (or never acquired) the practice of thinking or judging, and feels threatened by any request to consider anything."
Or, as I like to put it, an open mind is like an open trash can. People put garbage in it.