When I parrot this phrase to most people today they tell me the opposite is true, that any customer who isn't satisfied is an asshole and is doing you a favor if they switch to the competition.
I remember reading a business book in the early 2000s that said as much and that you should be trying to fire your worst customers. Around that time my stockbroker fired me as a customer because I didn't trade enough and because when they invited me to a presentation on annuities I asked why I shouldn't buy I bonds from Treasury Direct.
My reply to that is that there's a fine line between getting rid of your worst customers and getting rid of all your customers and it strikes me as another demented example of wishful hinking in "business as usual" like Best Buy's decision to stock a single Sony mirrorless camera body but not stock a selection of lenses to use with it.