Update (July 10, 9:00 a.m. ET): This piece has been updated throughout to reflect the resignation of Britain's ambassador to the U.S., Sir Kim Darroch.

Welcome to the world of diplomacy, Mr. Trump. It is a cruel place in which ambassadors and their staffs in Washington spend their days trying to squeeze secrets and strategies out of officials. They then cable them back to their capitals with frank, often not-so-glowing assessments.

It should come as no surprise that even ambassadors of our close friends sometimes say unkind things about us, as the recently leaked cables from British Ambassador Sir Kim Darroch made painfully clear. When the U.K. envoy relayed to his colleagues back home his unvarnished judgment that you are “inept,” “insecure” and “incompetent,” he was just doing his job.

I know you’re not a big fan of candid appraisals, but can I speak frankly here? This is Diplomacy 101.

I know you’re not a big fan of candid appraisals, but can I speak frankly here? This is Diplomacy 101. You, Mr. President, your team, and all those who go to fancy embassy cocktail parties in D.C. should know well how the game is played.

We diplomats don’t operate the way our friends at Langley do. We don’t bribe, steal or threaten. Our work is much more subtle. Every ambassador wines, dines and forges bonds with high-level officials looking for a morsel of gossip that is not yet in the news. Once obtained, they send it back to their ministry wrapped in trenchant analysis and gain brownie points for their terrific tradecraft. That's the work of diplomacy. It's pretty much been that way since the Peace of Westphalia in 1648.

This is literally what they tell you in the State Department’s orientation for foreign service officers — we used to call it “charm school”: “Thanks for giving a liver for your country.” You see, a big part of the job is spent drinking. Booze is one of the best friends you have as a diplomat; it’s often how you get other diplomats and foreign officials to open up. You remember your pal George Papadopoulous’ night out with an Austrialian diplomat in London? That’s the idea.

There’s also a standard playbook about how you manage or mitigate unflattering revelations from secret cables, now that Wikileaks has made their publication almost routine. It’s how we handled our own red-faced experience when Julian Assange’s website came on the scene: We spent countless hours pouring over old cables, trying to identify potentially damaging statements to try to minimize the damage.

As the British Foreign Office is doing now, we emphasized that diplomats needed to be able to offer honest assessments. They don’t always represent our policy, but it does ensure our leaders have our best insights and ideas. I mean, would you want your ambassadors to adore their hosts or advise you?

For the most part, our foreign counterparts understood the deal, even if they were unappreciative of our criticisms. And whatever their private feelings, they didn't dare send out recent tweets like yours calling the British ambassador "wacky" and "stupid" and "a pompous fool."

Here’s another lesson they should have taught you in first-year diplomacy: Attacking ambassadors for doing their job puts our own diplomats in danger. It sets a precedent that diplomats are fair game when they say something that displeases a leader where they are serving. I know first-hand what it feels like to have a foreign president call you out personally. An African coup leader and his cronies threatened me after I spoke out against their human rights abuses. Diplomatic immunity wasn’t going to save me if one of his supporters decided to take matters into their own hands.

The risks run high for America’s global influence, as well. If you want to penalize every diplomat for providing an honest take on the goings-on at the White House, you'll cut off relations with pretty much everyone. Since we’re speaking openly, who in this town, including your own chief of staff, hasn’t said a few critical things about your management style?

Still, if Darroch hadn’t decided to bow out Wednesday, booting an offending ambassador back home is an option. In Darroch’s case, he’d lost your confidence. You didn’t want to deal with him anymore. After all, he did undermine your administration’s standing with his government. And damage your ego.

There’s a political calculation you need to make in such cases, of course. Had you tossed out Britain’s ambassador, your buddy Woody Johnson, America’s Ambassador to the U.K., also would have likely gotten the heave-ho. Apologies for belaboring the point, but that’s diplomacy, Mr. President. It’s called reciprocity. They get to do to us what we do to them. You’ve probably seen some of this at play with your tariffs. And then you’d have had to get another ambassador vetted, confirmed and sent over to London.

If you want to penalize every diplomat for providing an honest take on the goings-on at the White House, you'll cut off relations with pretty much everyone.

Again, I'm taking liberties here, but I think that despite the political difficulties you would have faced from that course, it would have been the better one for U.S. national security. The fact that you instead forced Darroch to resign sends a very chilling message to ambassadors in Washington and abroad. Now they face the prospect that any time they offer counsel, even privately, they might face pressure to leave their post. This creates great instability in relations between countries. Any time you simply tweet about a diplomat you don’t like, they might have to go back to their home country. It does away with the time-honored process that has clear stages and formalities before such a drastic step is taken.

I could go on but my friends who are still working on the National Security Council tell me that you won’t read anything longer than a page, so let me offer a Reader’s Digest summary. Love letters and tweets do not a foreign policy make. You have to invest in relationships that allow for hard truths to be expressed. Finally, diplomacy is a two-way street. So I’d advise driving with some degree of caution while honking America First and telling others to get off the road.