"What is a 'textbook' business strategy that completely falls apart in the real world?"

[Cassy micheal]

Business books and MBA programs love to hand us clean, glossy formulas: always optimize for scale, never compete on price, obsess over every customer metric, pivot fast, build a massive social media presence.
And yet, in the trenches, some of the most successful (or disastrous) decisions completely ignore the rulebook.
I'll start: The classic advice to "scale as fast as possible once you find product-market fit." In theory, it sounds like winning. In reality, I've watched brilliant companies light millions of dollars on fire trying to scale a leaky bucket, prioritizing vanity growth over actual operational stability, only to collapse under their own weight.
What is a piece of golden business or career advice that you've found to be absolute nonsense once you actually tried to apply it?