A judge gives the verdict to the prisoner that he will be hanged one noon next week, on a weekday, but the day would be a surprise. The prisoner goes back to the cell and makes the following assumptions.
If the executioner doesn’t appear by Thursday noon, he will not be hanged as the last day, Friday, is no more a surprise. After eliminating Friday, he extends the logic to Thursday, which now becomes the final day. Finally, he concludes that he will not be executed as none of the days will come as a surprise.
The prisoner is happy and confident that he will not be hanged, only to find out by complete surprise that he was executed on Wednesday at noon. The judge now stands correct; it was a surprise to the convict. But what was wrong with his logic?
