Working it

Leaving the newsagency with the papers yesterday, I overheard an interchange that went:
"Don't work too hard."
"That's an oxymoron."
"What?"
"Don't work too hard. You can only give what you have - so you can never work too hard."
Worked for him - and it makes sense too ... but those people who talk about giving 110% may wish to take issue with it.