The superstious belief that when given a list of like or similar minor tasks to be completed in order, the last repetition will invariably the most difficult or impossible to complete - in contrast to the preceding tasks that were completed with ease.

Originated in teh Irish section of Boston, Massachusetts called Dorchester.
The final screw could not be driven completely into the wall, after continually trying, the screw was worn to the point where the driver could not bite it. The capenter sighed and said out loud, "thompson's law".
by Paul Ameradeus October 3, 2006
Get the Thompson's Law mug.