Brandolini's law

Brandolini's law, also known as the bullshit asymmetry principle:

The amount of energy needed to refute bullshit 
is an order of magnitude bigger than that needed to produce it.

So your effort to debunk misinformation may be at the mercy of someone just spouting semi-coherent nonsense, and will be wasted effort when they care about loudly being right in their own way, more than about it being actually true without them being loud about it.

So it's often worth it to figure whether they will listen to you at all, perhaps to point out where burden of proof lies ("I will doubt your statements until you can show me any proof").

https://en.wikipedia.org/wiki/Brandolini%27s_law