The most dangerous phrase in the language is, “we’ve always done it this way.”
"Come on, let’s mix it up!" The heart surgeon says.
"B-but we’ve always done it this way!" The other replies, "this is how you replace a heart valve."
"That’s the most dangerous phrase in the human language!" The first surgeon replies haughtily as he inputs a fruit loop into the patient’s heart. "This will be his valve. He will be a fruit loop in a world of Cheerios."
(taken from this post on the experiments of Harry Harlow)
This is serious business, because this is a large part of how sexism, racism, homophobia, rape culture, ethnocentrism, etc. continue to happen.