I think IntravenousDemilo might be correct...
According to Dictionary.com:
carrot and stickReward and punishment used as persuasive measures, as in Management dangled the carrot of a possible raise before strikers, but at the same time waved the stick of losing their pension benefits. This term alludes to enticing a horse or donkey to move by dangling a carrot before it and, either alternately or at the same time, urging it forward by beating it with a stick. However the Word Detective has something interesting:
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Dear Word Detective: I am puzzled by the usual use of "carrot and stick." It is most often used in a context that suggests a strategy balanced between reward (the carrot) and threats (the stick). I always thought it referred to a phantom reward, however, as in the carrot dangling from the end of a stick hung in front of the donkey to keep it moving forward in its perpetual --and necessarily failed -- effort to reach the carrot. -- Robert Fleming, Tucson, Arizona.
Well, if it's any consolation, you are not alone in your puzzlement. Precisely the same pesky little question has been nibbling at the back of my mind for years, busily shredding useful information (my cell phone number, shoe size, etc.) to useless tatters in the process. I'd set traps, but I cannot abide the feel of cheese in my ears.
Furthermore, you and I seem to have quite a lot of company in our quandary. I have checked at least fifteen usually useful sources for the skinny on "carrot and stick" but few even mention the phrase. The Oxford English Dictionary seems to endorse the "reward and threat" interpretation, explaining the phrase as being "with allusion to the proverbial method of tempting a donkey to move by dangling a carrot before it … an enticement, a promised or expected reward; frequently contrasted with ‘stick’ (= punishment) as the alternative."
Yet the earliest (1916) citation for the phrase listed by the OED seems to refer to a carrot dangling from a stick attached to and moving forward with the donkey itself: "The spectacle of an otherwise intellectual individual engaged in trying to plumb the depths of duplicity to which dealers can descend in faking old furniture is like that of the donkey pressing eagerly forward after the dangling carrot. It would ... be very pleasant to possess the carrot of complete knowledge, but the conditions render it impossible."
Word Detective****
I am inclined to think he is right. I am inclined to think that the OED, if the first citation, is this metaphor, then the 'current' idiom of using a 'carrot and stick' (the way I did) derives from this metaphor and not the other way around, as I was told once.
It makes sense, as contrasting 'pleasure' and 'pain' for this or any example could very well use other types of contrasts to make the same point. (honey and vinegar?) However, the practice of using these particular two words together probably did have it origins when combined to make a donkey, do something he would not otherwise do, for a reward that he will never get.
The media probably ruined the original metaphor through simplication (which it doesn't constantly..no arg there)...
I would imagine a tale of futility like the metaphor of the donkey, stick and carrot probably finds it's inspiration farther back still...
TantulusTantalus was the son of Zeus and was the king of Sipylos. He was uniquely favored among mortals since he was invited to share the food of the gods. However, he abused the guest-host relationship and was punished by being "tantalized" with hunger and thirst in Tartarus: he was immersed up to his neck in water, but when he bent to drink, it all drained away;
luscious fruit hung on trees above him, but when he reached for it the winds blew the branches beyond his reach.PantheonI'll give him his point...