Everyone can tell when someone is fronting and faking confidence, or faking being humble, nobody is fooled.

The folks who do it badly tend to stick out. But this is far more useful on the margins, where a firm's performance is genuinely not well-understood.

Companies understating/overstating their expected earnings to manipulate their stock price is a time-tested means of legalized insider trading. Firms, like Apple, used to do an exceptional job of sitting on products in development until the last moment, generating all sorts of ambient hype whether or not they had anything to brag about releasing. Warren Buffet's Berkshire Hathaway is a textbook case of "talk small and carry a big balance sheet" and routinely outperforms its competitors as a result.

Exploiting gaps between your perceived and actual value is functionally how value-investors make money. If nobody ever got fooled, equities would never value themselves different from the perfectly predicted book value.