In an internet discussion, opponents will only ever respond to your weakest point.
So don’t give an off the cuff example, because you’ll end up discussing that one thing for the rest of the thread. In fact, examples of any kind are dangerous, because real life is complex: there’ll almost always be some insignificant part of any example that doesn’t overwhelmingly illustrate your point. And again, that’s what you’ll be discussing from now on.
And, when you do, your opponents will be revelling in the non semper ergo numquam fallacy: thinking they can shoot down your argument if they can disprove any part of it, regardless of how slight the technicality.
If your opponent is reasonably antagonistic to your position, there is very little point in trying to break this law. Because this is a prisoner’s dilemma: if you discuss reasonably and your opponent follows Duncan’s Law, you will just sound like you’re conceding. And your reasonable language will get thrown back at you from that point on, as evidence of your concession and perhaps duplicity.
The more two parties engage in this, the more likely they are to descend into insults and acrimony. Because both of them feel that their position is being belittled, they are being ignored, and the other party is arguing in bad faith. Because, they are. It is easy to identify it in the other person, but almost impossible to notice how much of an ass you’re being yourself.
If two parties end up insulting each other, you can usually trace it back to Duncan’s Law. At some point, each felt the other was not properly engaging with their position, but instead grandstanding on trivial sideshows.
This is why many internet discussions go so badly.
This is why people who gamely try to engage on their opponent’s blogs end up sounding like trolls, or being made to feel so unwelcome that they leave.
The law also applies to some forms of scholarship, but perhaps the long lead time makes it less pronounced.
I do this, particularly with creationists. Do you?