Tevye sings that line in Fiddler On the Roof and it is more than true. More because when you’re really, really rich, it’s not just other people who believe it; you think you really know. And yes, I am talking about Donald Trump.

I have known several successful people, and one personality trait they share is the belief that they have accomplished so much they must be right. Part of this comes from the success they have had, but even more importantly, it results from other people reinforcing it. After all, who was going to tell Hugh Hefner how foolish he looked holding business meetings in his bedroom at 6 pm while lounging in his PJs. (Yes, I was there so I know it’s true.)

And so these highly successful people dismiss that voice in their head that asks “Are you sure you want to say that?” It’s a filter important for all of us, but it’s critical for a public person. And that’s why Trump does and says the things he does.

So he makes off-the-cuff comments like this to the Jewish Republicans:

“I know why you’re not going to support me. You’re not going to support me because I don’t want your money …Look, I’m a negotiator like you folks, we’re negotiators.” “This room negotiates deals; perhaps more than any room I’ve ever spoken to.”

That inner filter would have told him he was repeating anti-Semitic stereotypes. He’s not stupid, just acts like it because his sensitivity filter isn’t working.

And his comments strike women as demeaning. I don’t know whether he meant to imply Megyn Kelly was menstruating when he said she had blood “coming out of her wherever,” but that inner voice would have told him to beware because that’s how many women heard it. Hispanic “rapists?” We don’t need more examples.

Trump has no filter because he doesn’t think he needs one, so his ad lib remarks make him seem ridiculous, but he doesn’t hear the chortling. Does he really think that his father’s million dollar “small loan” to get started in business was anything more that the tip of the silver spoon sticking out of his mouth? How much he looks like former Texas Gov. Ann Richards description of George W. Bush, “born on third base and thought he hit a triple.”

Remember H. Ross Perot telling an African-American group “You people…?” Guaranteed they stopped listening to whatever came next.

New York Times columnist Thomas B. Edsall quotes Psychology Prof. John Gartner on what he calls “the hypomanic edge,” which certainly seems to describe the GOP frontrunner.

“He is flooded with ideas. He is driven, restless, and unable to keep still. He channels his energy into the achievement of wildly grand ambitions… He feels brilliant, special, chosen, perhaps even destined to change the world. He can be euphoric. He becomes easily irritated by minor obstacles. He is a risk taker. … He sometimes acts impulsively, with poor judgment, in ways that can have painful consequences.”

Such people may compel loyalty and support, Gartner says, but this can also lead “to impulsive behavior (ready, shoot, aim) and confident leaders who glibly take their followers over a cliff.”

And just as Perot took his people over a cliff and elected Bill Clinton, GOP leaders fear Trump will do the same for Mrs. Clinton. So beware of people who really know. Beware of people who are out to prove they know more than anyone else.