A grocer puts up a sign about his turkeys: $5 each or $20 for three.
All day long, people approach him to express their outrage at his incorrect math.
“It should be $15 for three! I’ll just buy them separately.”
At the end of the day, one of the grocer’s employees asks if they should fix the sign before they open again in the morning.
“What do I need to fix?” the grocer asks. “Before I put up the sign, nobody would’ve bought three turkeys at once.”