Life is substantially easier when you're told what to do. Sure it's a bummer losing the free will that allegedly separates us from the beasts in the field and the robots in the robot factories, but doing what you're told, in spirit if not deed, delivers you from the consequences of your actions. You went to college, you worked hard, you met the right people; you should be successful. It's too bad that old models no longer work in the current climate.
And so it goes with nagging. I once compared nagging to torture in terms of both its efficacy and morality, and I have long felt that value of a nag-induced errands, chores or lifestyle choice is seldom worth the long-term effects. The downside of any successful nag is a bubbling cauldron of resentment and a lifetime of selective hearing. The guy (or lady!) you're hectoring into doing things that are probably in his (or her!) best interests will likely begin the habits of A) keeping the TV entirely too loud to prevent this little voice from constantly barking instructions and B) grinding teeth into little enamel nubs. For the record, you can both ask someone to do something for you and how you’d like it done, you can’t, however have them want to do it.
But here's the rhubarb, like dumping DDT on crops, nagging works really, really well in the near and narrow-term. It's binary. First of all, repetition, especially tautology, burrows a hole in even the stoutest of defenses. Propaganda (Mitt Romney hates women and Barack Obama hates capitalism) starts making sense when repeated often enough and with enough subtle variation. This policy once led to the frenzied invasion of Poland. And second-like, the greatest human motivation is not the acquisition of pleasure; it's the abatement of pain. Nagging works because saying "yes" stops the ear assault. Is using annoyance to Hulk-smash your loved one into submission really victory?
Unless you're a sadist, henpecking can't be any more fun than being henpecked. Relationships, even the really good ones, aren't all iced cream, puppy breath and mutual orgasms after precisely the right amount of foreplay. Being the bad guy (or gal!) stinks like fish-flavored candles.
In summary, if you absolutely must nag, do so only when absolutely necessary and don't be surprised when his (or her!) bros hum a few bars of the one Devo song anyone knows when you stomp into a room.