You participate in a game show where you must choose between 3 doors. Behind 2 doors is a goat, but behind 1 door is a car. You pick a door, say door no. 1, but before you open the door, the host opens another door, say door no. 3, which has the car behind it. "Oops," says the host.
You lose.
Or that the car and goat are already behind a door. There may be nothing behind any of the doors until you choose; they're always wheeling stuff around behind the scenes in game shows.
The answer in the original Parade magazine column way back relied on assumptions not stated in the description, and the smart people coming up with the 'wrong' answer just had different assumptions.
The author of the column went by a pretentious "vos Savant" assumed name and lied about her credentials; she claimed to be in the Guinness Book as highest IQ, but was never the record holder at the time of publication and the one year she was listed was for a test taken when she was like 3 years old. The whole column was a sham.