Flogging A Dead Horse

In the days of sail, Isil says, a sailor customarily received his first month's pay in advance. And he customarily managed to spend it all before coming aboard. Consequently for the first month at sea most sailors felt as if they were working for nothing. Admiral William Smyth observed that trying to get wholehearted work out of the crew during the first month at sea was as much an exercise in futility as "flogging a dead horse."

I feel like that now. Uncle Sam has taken my next month's wages and I've lost the will to work.

What's the use? The money's already gone.