Contract bridge is quite a complicated game. Suits, contracts, overtricks, bidding conventions, and...ack! Now some dweeb (usually you) has accidentally played an illegal card and wants to take it back! Should you let 'em? This is, after all, a national tournament.
Well, thanks to the Laws of Contract Bridge, you don't have to decide. You just holler, "Director!" and this nice man (or woman) will walk over, armed with a several-hundred-page book of rules known as The Laws of Duplicate Contract Bridge, listen carefully to your predicament, and tell you what options are available.
"Hmmmmm, well, yes, East's play was certainly illegal. Law 50 says, (because we don't want people to have Unauthorized Information about that card East tried to play) East has to play that card at her next opportunity." And then nobody gets to argue about it. That, and the Zero Tolerance rules, are why you find nice people playing bridge instead of grumpy nitpickers.
Thank goodness for the director and his ginormous book of rules, 'cause otherwise it would be impossible to have any kind of fair game of duplicate bridge.