By now, Americans — regardless of which side of the aisle they sit — have noticed one thing about this circus of an election season: Say one thing against Republican presidential candidate Donald Trump, and get ready for a slew of sarcastic tweets, snide missives, and blatantly insulting attacks on character.

And people have noticed. The New York Times has a running list of insults he’s slung and Twitter is on permanent standby for the next outrageous thing the Donald will say.

It’s something that Democratic presidential candidate Hillary Clinton is hoping to capitalize on for her campaign as she tries to paint Trump as impulsive and childish, a point she emphasized in her acceptance speech at last week’s Democratic National Convention in Philadelphia:

So just ask yourself: Do you really think Donald Trump have the temperament to be Commander-in-Chief? Donald Trump can’t even handle the rough-and-tumble of a presidential campaign. He loses his cool at the slightest provocation. When he’s gotten a tough question from a reporter. When he’s challenged in a debate. When he sees a protestor at a rally. Imagine, if you dare, imagine — imagine him in the Oval Office facing a real crisis.

And then she offered this quote that’s since been repeated by people looking to sum up her speech:

A man you can bait with a tweet is not a man we can trust with nuclear weapons.

Khizr Khan, father of deceased Muslim U.S. Soldier Humayun S. M. Khan, holds up a booklet of the U.S. Constitution at the Democratic National Convention on July 28. Getty Images / Alex Wong

Turns out, it didn’t take a tweet that night to bait Trump. All it took was this speech from the father of a slain Muslim-American soldier who died from a car bomb in 2004, before Trump felt cornered. That very weekend, Trump went on the airwaves, first on an interview with George Stephanopoulos on ABC, to suggest that Ghazala Khan, the mother of Captain Humayun Khan, was silenced because she was a Muslim woman.

Here’s Trump on Sunday morning:

Perhaps still fuming, here he is again, a half-hour later:

Political pundits are a bit puzzled by Trump’s responses — he could have just let it go and hoped the media would eventually move on to other, less sensitive topics, but Trump just couldn’t resist one comment after the other.

Which insinuates a different question: Why can’t Trump just let it go?

It’s been widely documented that Trump is probably a narcissist: Running for higher office is potentially a way to feed his ego and conquer attacks on his own character. As Jeffrey Kluger, author of The Narcissist Next Door: Understanding the Monster in Your Family, in Your Office, in Your Bed—in Your World, wrote in TIME:

The petulance of Trump’s public feuds — with Rosie O’Donnell (“a total loser”), Seth Meyers (He’s a stutterer”), Robert De Niro (“We’re not dealing with Albert Einstein”) and Arianna Huffington, (“Unattractive both inside and out. I fully understand why her former husband left her for a man . . .) — is wholly of a piece with the fragility of the narcissistic ego. In Trump’s imaginings, it is Fox News’s Megyn Kelly who owes him an apology for asking pointed questions during the Republican debate, not Trump who owes Kelly an apology for his boorish behavior and school-yard tweets (“Wow, @megynkelly really bombed tonight. People are going wild on twitter! Funny to watch.”). As for his sneering misogyny — his reference to blood coming out of Kelly’s “wherever?” Nothing to see here. It’s Jeb Bush who really should apologize to women for his comments about defunding Planned Parenthood.

Kluger points out that a narcissist personality type like Trump might have a difficult time accepting criticism and apologizing for running off-course because an attack on their ego is an attack on their very being, which means it’s the commenter’s fault that they provoked a racist/misogynistic/disturbing response from Trump, not Trump’s. Twisted, right?

But there’s probably more to Trump’s inability to just let a slight be — and he’s not the only one who has trouble living according to the “let it be” mantra of life. We all know that one person who can’t seem to let it go, who holds onto grudges and lashes out at the slightest provocation or slight — maybe it’s your crazy uncle that can’t help but stir up a fuss at Thanksgiving, or a toxic friend/flame that receives any criticism as a personal offense.

As you might have guessed, there’s a certain type of human mind that gets oddly attached to slights and has the constant urge to retort.

In his book, A Slap In the Face: Why Insults Hurt — And Why They Shouldn’t, philosophy professor William Irvine points to our evolutionary desire to be up top and win, which he calls a social hierarchy game. Some people have this instinct more than others, and it might just be that Donald Trump has an insatiable urge to come out on top, a competitive streak gone rogue. Irvine suggests that this constant need to insult others to maintain his own rank as top dog is not just reminiscent of wolf pack behavior but also probably contributing to a degree of anxiety that fuels itself in more insults.

Furthermore, Irvine’s research on insults finds a unique brand of retorting back called the second-hand insult — where a person’s insult is blamed onto a third party — to be especially debilitating for both insulter and insultee. “It’s a way of inflicting pain on somebody, but with complete deniability,” he told Wright State University. “We want to put other people in their place, and this is a safe way to do it.”

A December 2008 study published in the journal Psychological Science titled “Reciprocity is Not Give and Take: Asymmetric Reciprocity to Positive and Negative Acts,” suggests there’s a certain type of person who can’t follow Frozen’s Elsa’s advice to just “let it go.”

The University of Chicago professors set up a series of games where people were asked to share money or take the whole bounty. Those who took were looked down upon (rightly so, probably, it’s basically pretty selfish) but the more interesting aspect of the study was the response of those who felt they had had something taken from them: “Our experiments demonstrate that social exchange is based largely on the meaning of social actions, rather than on the objective value of those actions,” the authors write. “Positive actions of giving are reciprocated in comparable measure, whereas negative actions of taking are reciprocated more selfishly and may be followed by escalation.” In plain English: If you are praised for some action, you’ll respond in kind. But hell hath no fury as a person (or Trump) scorned.

In which case, might we suggest taking some Tylenol? Yes, that over-the-counter drug that eases fevers and soothes a headache is also an effective anger management tool, at least according to a team of psychologists whose 2010 research was published in Psychological Science. The thinking goes like this: Pop a couple acetaminophen tablets — the active ingredient in Tylenol — and your heart might ease up on feeling hurt. This, of course, isn’t a suggestion to OD on Tylenol if you’re particularly pissed off, but it’s a nod towards the fact that the phrase “broken heart” has some physiological basis.

And if Trump’s heart is palpitating after being called names, it might be something worth considering.