Handicap Principle
the flex only works because it's costing you something real
Grounded in the research on Wikipedia: Handicap principle; Amotz Zahavi (1975), 'Mate selection—a selection for a handicap', Journal of Theoretical Biology
the move
You prove something is true by showing you can afford the cost of NOT hiding it. A signal is only believable when faking it would wreck you. The handicap itself is the receipt: carrying a disadvantage you clearly survived says you've got resources to spare. Words are free, so they prove nothing. A self-imposed burden you're still standing under proves plenty.
the first effect
Biologist Amotz Zahavi named it in 1975, studying why peacocks grow tails that should get them killed. His answer: the tail is honest BECAUSE it's a liability. Only a genuinely strong bird can drag that thing around and still dodge predators. A weak one would already be dead. The cost isn't a bug in the signal, it's the entire mechanism that makes it impossible to fake.