the illusion of choice between 

giving simple instructions (sign on the card reader at the checkout counter says USE THE PEN, leaving the customer uninformed as to the reason for the rule and therefore its parameters and where its exceptions are, so they assume this is the exception and they tap the screen with their finger instead of the pen) 

and giving detailed instructions (sign says THIS CARD READER IS GLITCHING AND IF YOU TAP THE “APPROVE” SYMBOL WITH YOUR FINGER INSTEAD OF THE PEN IT’S GOING TO MISINTERPRET THAT AS YOU TAPPING THE “CANCEL” SYMBOL AND WE’LL HAVE TO START THE TRANSACTION ALL OVER AGAIN SO PLEASE AVOID THAT BY USING THE PEN, at which point the customer got tired of reading about five words in, and just taps the screen with their damn finger anyway)