A person that works below me recently initiated a workplace dispute with me regarding a technical matter and my advice was ultimately acted upon by the boss. Since this time, the co-worker has been less productive in carrying out the assignments I've designated for him. Specifically, he has been slower to respond to my request and seems to be "playing dumb" when I ask him questions.
What can I do to remedy this situation? Have I permanently damaged this relationship?
I'm assuming you're this person's manager (or at least team leader) because you talk of them working below you, but you also talk about them being a co-worker.
A couple of thoughts spring to mind. Firstly as a manager, stop using and thinking the term "won" or "win" in regards to a dispute with someone who works for you. You're there to lead the team, not win arguements and if you give any slight impression that you think in terms of "wins" against your team members then you will always have problems with your team.
Secondly, if they're invested in doing things one way and you're now requiring them to do it a different way and/or they have any perception that you think "I have won" then of course they're going to be upset and of course this might manifest itself as behaviour akin to sulking. If you stop picking at the 'scar' then this will fade over time.
The problem really happens when their job performance is affected by their 'sulking'. Here my first thought would be to make it clear to them that they are under-performing and that they need to fix that problem. This may not always work well depending on the type of person they are, of course, but it's good place to start.
Don't tie it to the previous dispute because that's not relevant to their performance issues now. If they want to discuss the other issue then that might be fine if it helps to clear the air but you need to make the point that what happened in a dispute before is not relevant to their performance in the future.
Just have a talk with him. Don't be agressive, but firm. Something like "Look, I feel like things have been a little tense between us since our dispute about X. We didn't agree on this point, but that shouldn't keep us from working efficiently together. I respect your work and opinion, so let's put all this behind us and get back to work." (phrasing is far from perfect I guess, English not being my mother tongue, but you get the idea).
After that, two things can happen : either he gets his shit together, and problem is fixed, or he keeps on "playing dumb". In that second case you have a problem that probably needs to be adressed by your manager. Point being, if you let things as they are it won't get better, your work quality will decrease and it's gonna come back and bite you in the ass at some point. You can't let that happen.
Note : The answer above assumes you didn't get the wrong idea about what's going on. Maybe, and it's your best case scenario, he got over it and latest performance issues aren't related to your former dispute.
You need to exercise due diligence and make sure through a third party, say your manager or another person, that the cause of his sulk is the outcome of his dispute with you. There may be other things going on in his life that you are totally unaware of, that would cause him to sulk. His losing the dispute and subsequent sulking are correlation. Correlation is not necessarily causation.
Let's assume that you have determined that the cause of his sulk is indeed the outcome of his dispute with you. Have a third party with weight,authority or influence such as a manager talk to him. Have the manager thank him for getting in a dispute with you, because it shows that he does care about how he does his job and the welfare of the firm. Then the manager should tell him that disputes are healthy as long as the disagreements are genuine and that some really good things have been born from disputes. The fact that he lost is not a negative reflection on him, because he fulfilled his role as devil's advocate on behalf of the firm. And that the firm is better off from the dispute haven taken place. You probably shouldn't be the one making the point, as his feelings toward you may be too raw.
Let the point sink in into his head, and give it some time for the point to settle there. Let him get over his tantrum. It would be a tragedy if he didn't get over his tantrum. For him.
Whether he uses the slack you're cutting him to heal his ego or as the rope to hang himself with is his own choice. If he heals, he will probably heal faster on his own than if you tried to "help" with some intervention of your own.
Reminds me of a Zen story (*). You let go of that dispute a while ago - with no prejudice to either you or him, but he is still carrying it on his back. If you show him through you actions that you were not emotionally involved in that technical dispute, he might see that it was silly of him to make an emotional investment on that technical dispute. And in general, it is silly to make emotional investments in technical disputes. If he drops the emotional investment he made in that dispute, he will find his way out of the fact that he didn't win. But it's up to him to drop that emotional investment, and no one can make that choice for him. From your point of view as his superior, either he gets over that dispute however he does it and he keeps his job or he doesn't get over that dispute and he doesn't keep his job. It's not complicated and there is no need to make it complicated.
(*) Two monks were on a pilgrimage. One day, they came to a deep river. At the edge of the river, a young woman sat weeping, because she was afraid to cross the river without help. She begged the two monks to help her. The younger monk turned his back. The members of their order were forbidden to touch a woman.
But the older monk picked up the woman without a word and carried her across the river. He put her down on the far side and continued his journey. The younger monk came after him, scolding him and berating him for breaking his vows. He went on this way for a long time.
Finally, at the end of the day the older monk turned to the younger one. "I only carried her across the river. You have been carrying her all day."
