Sure enough, you can pick pretty much any episode on the show and see this rule at play. When Charlie writes a whole musical in his attempts to woo The Waitress in season 4, we believe that Charlie genuinely thinks this is a solid plan to win her hand in marriage. We also see this feverishly intense belief of his in the way he turns into a theatre diva behind-set, refusing to handle criticism from the rest of the gang and screaming at Dee when she asks for reasonable script changes. We understand what Charlie wants to achieve — a musical so beautiful that it melts away years of The Waitress’s resentments towards him — and we can see the reality of what he’s making: a shoddy musical about a kid (maybe) getting molested, one that makes Charlie look like a total creep. Part of Charlie is aware of the dissonance here, which is why he’s so unusually high-strung throughout the episode.
Maybe the best example of this rule is the season 16 storyline where Mac tries to manipulate Phillies player Chase Utley into playing a game of catch with him. It’s a scheme that involves inventing a fake dead child and (for some reason) suddenly switching to a questionable British accent. Like Charlie in “The Nightman Cometh,” this is some deeply bizarre behavior, but it never feels like the show’s just being zany for zaniness’ sake. Mac has had a long-established desire to get himself a loving father figure, and a game of catch with Chase Utley would be a temporary fulfillment of that dream. Yes, Chase Utley is technically younger than Mac, but that’s irrelevant.