I hate that phrase so much.
It sole purpose is to belittle and dismiss the person you are talking to.
It tells the person that they are obviously unable to understand because of some unrelated trait. It’s an ad-hominim that just shuts down the conversation.
It’s only used by people that cannot actually defend their position, but rather than continue to discuss it, they would rather just shut out the other person.
It’s them telling the other person “you are less than me which is why you are wrong, and you must simply accept that because you cannot possibly understand how I am right.”
My response would be that if you cannot explain your position, then you cannot defend it, and therefore you do not understand it yourself. This implies that you are simply feeling you way into your position using gut instincts, which are easily created and manipulated without a reasonably sound argument. An ad on TV, a op-ed piece only half heard, a slew of biased headlines, and more all contribute to these gut feelings without providing a rational base.
In short, I reject your claim that complicated positions cannot be explained. Yes, many can’t be easily explained, but you should still be able to explain and defend them.
So when the position is challenged and you can’t defend it because you have only these gut feelings at the core, you fall back on the belief that anyone would have the same feelings eventually. This is, of course, not true.