The natural phenomenon that occurs when one enters any Wal-Mart Superstore needing nothing, yet somehow ends up leaving with a full cart.
This is probably due to their low costs, extended store hours, and poor employee benefits.
Victim: Dude, help me unload my cart.
Victim's Friend: I thought you said you didn't need anything?
Victim: ...They did it again! It's The Wal-Mart Effect, Gets me every time.
Victim's Friend: Ah, I see what you did there. Very well played, Wal-Mart.