Fred can never lose weight.

geotrice

Fred is overweight. If a person is overweight, one more day of eating at a deficit will not cause them to suddenly not be overweight. Therefore Fred can never lose weight.

It's a continuum fallacy, also known as a fallacy of the beard, fallacy of the heap, or in this case fallacy of the fat.

The argument against this fallacy is of course that for each day Fred eats at a deficit, the degree to which Fred is overweight changes slightly and that each slight change adds up to weight lost, eventually shifting Fred from overweight to ideal weight.