When people find out you're an expert in X, they often say things like "Since you're an expert in X, of course you must know Y." And then when you hesitate about Y, they think you're extremely stupid because you don't even know a basic fact in your area of expertise. The supposed fact Y is really just a common misconception, but you can't convince the non-expert of this. A: Since you're an expert on perfumes, of course you know the right way to apply them is to spray a mist into the air and then walk through it. B: Umm A: What?! You don't even know that?! Hahahahehehe. B: Uhh, you can't know what's not true. A: Everyone knows that hahaha! B: Everyone is wrong. A: How can you not even know that?! Whoa man, you call yourself an expert?!