If work is applying your ability, then hard work is applying your ability with focus and intensity to the exclusion of other possibilities:

☛ Farming is hard work because you can not take a vacation in the summer.

☛ Extreme programming is hard work because your customer, your group and your partner all direct your attention.

☛ Cheating on your spouse is hard work because you can never relax and just be yourself.

☛ Writing wiky is easy work, perhaps the easiest writing of consequence ever invented.