Is sex all pleasure?

The Commanding Officer of a regiment in the U.S. Marine Corps was about to start the morning briefing to his staff, battalion and company . 

While waiting for the coffee machine to finish its brewing, the colonel decided to pose a question to all assembled.  He explained that his wife had been a bit frisky the night before and he failed to get his usual amount of sound sleep. He posed the question of just how much of sex was work, and how much of it was pleasure?

The regimental executive officer chimed in with 75-25% in favor of work.

A captain said it was 50-50%. 

The colonel's aide responded with 25-75% in favor of pleasure, depending on his state of inebriation at the time.

There being no consensus, the colonel  turned to the private who was in charge of making the coffee.  What was HIS opinion?

Without any hesitation, the young PFC responded, “Sir, it has to be 100% pleasure.”

The colonel was surprised and, as you might guess, asked, why? 

“Well, sir, if there was any work involved, the officers would have me doing it for them.”

The room fell silent.