This is on the danger of pushing it too far. It is a delicate business knowing what the moment will allow. You can be right in intent and wrong on execution, and if you’re wrong on that it may not matter you were right in intent. A great woman in business and the arts once told me the most dangerous place to be is significantly ahead of the curve. People will dismiss you as too far out. Better to be just a little ahead of the curve, which allows people to wonder if you might be a visionary. She in fact was a visionary, and careful not to seem too many steps ahead.

A great challenge in politics and diplomacy is to see in real time the line between the opening that should be pursued and the trap that must be avoided. And, once you’ve made that calculation, not to push things too far. It can be delicate. You have to be like a safecracker who files down his fingers so he’ll feel every click.

China pushed Hong Kong too far the past few years, bullying it, trying to pull it into a closer, more smothering political embrace. Hong Kong pushed back. Are the demonstrators now pushing it too far? I hope not but fear they may be. They’ve already won — humiliating the chief executive, who this week backed down on the issue that sparked the rebellion, and embarrassing China, which found itself with a World Opinion Catastrophe on its hands. The demonstrators made a statement, successfully — not easy to do in this world. They asserted certain implicit boundaries for Chinese behavior. They gave it a warning: push Hong Kong around and the price will be unrest and humiliation.

The protesters have sustained their demonstrations and vow they will continue. They demand firmer autonomy and more democracy. China, angry at the disruptions, some violent, and shutdowns, had already moved forces closer. Will Beijing again push things too far? Will it intervene militarily? Is a collision with world-wide implications coming?

I hope the demonstrators know what they’re doing and aren’t pushing it too far.

The Democratic presidential candidates are pushing it too far. No left-wing idea is too much. Nothing, no sense of political reality, is hemming them in. They are like progressive Barry Goldwaters: Moderation in pursuit of justice is no virtue. The president meanwhile is so crazily taken with his own power that he redraws hurricane maps.

Everyone is pushing it too far. My way of explaining this to myself is that everyone now making decisions grew up in the past 60 years, a time of historic wealth creation, human growth, relative stability. And they can’t help it, they think this is normal. They think life is nice! They’ve lost a tragic sense about history. They often accuse those who disagree with them of being on “the wrong side of history,” as if it has a side, as if it flows ever upward.

It’s odd but in this cynical age they’ve grown too trusting of good fortune.

They assume no one will, through accident, miscalculation or madness, launch a nuclear missile. They assume these robots we’re inventing, the artificial intelligence, will ultimately be benign — the authorities will make sure they don’t make life monstrous. And so the busy geniuses in their genius campuses, all born in stability, mostly born in a postpatriotic and post-Christian West in which old loyalties not only lessened but came to be seen as wicked, are doing their thing, largely unregulated and in secret.

Don’t you think it will all turn out well and only benefit mankind?

No. You think they’ll push it too far.

One thing I miss is the Professional Worriers who populated previous generations in government. They were a special type in foreign affairs, men who were by nature concerned that some international move or eruption would result in “heightened tensions” and “instability” and who counseled “prudence.” They were usually veteran diplomats. They were extremely boring. They were always cautioning. They were worth their weight in gold. They didn’t trust history — they’d seen it go bad before World War II, in Korea and Vietnam. So they were careful. They never wanted to push it too far.

I end with Britain and the Brexit saga, which turned chaotic this week in Parliament with a series of defeats for the new prime minister, Boris Johnson, and defections and expulsions on the Conservative side, including the resignation of Mr. Johnson’s brother.

What a lot of wreckage.

A real crisis isn’t about “someone will lose and someone will win”; it’s about “something will be changed — a reality that reigned in the past won’t be reigning anymore.”

Brexit is a real crisis.

The cultural composition of the Conservative Party is being changed. Out are the great and stately — Winston Churchill ‘s grandson Nicholas Soames and former Chancellor of the Exchequer Kenneth Clarke. In are the crazy-haired and bodacious, technocrats and internet gurus. Out is austerity, in is high spending. All this echoes changes in American conservative thinking and style.

When Boris Johnson was elected I wondered: Is he the brute and brilliant force who can resolve this thing? Is he the only animal big enough to fight European leaders who will do anything to stop the jailbreak?

This week the only question was: At this extraordinary moment is Boris playing some grand and subtle strategy only he can see? Or is he flying by the seat of his pants, making it up as he goes along. Is he operating on anything that might be called a plan?

The question reached one of his most committed parliamentary supporters, who replied: “Bismarck never had a plan, he always improvised.” Meaning, I think: Mr. Johnson doesn’t have a plan, sometimes you can’t make one.

His objective isn’t wrong. A great nation cannot be at its own throat forever. Britain has endured destructive uncertainty for more than three years. Enough: It must be one thing or another, in Europe or not. The voters chose not. Exactly how Britain leaves it must be legislated.

Leadership in such a moment needs not only wit, presence and charisma, which Mr. Johnson has. It requires judgment, trustworthiness — that people have confidence in your thinking, your word. It is in those areas that Mr. Johnson fails.

Almost everything he did this week looked like pushing it too far.

A month ago he seemed the solution. He looks now the problem.

At this point Mr. Johnson should remember that politics is a game of addition, not subtraction, and limit the wreckage of the past week by taking back into the party those he threw out.

Sooner or later he’ll get the election he’s asking for, and it will likely put him against Labour’s Jeremy Corbyn, whose ideology amounts to a daily pushing-it-too-far. Mr. Johnson would be the favorite. Britain is always stronger than it thinks: It has a thriving economy and tough, capable economic players. And as it showed when Mr. Soames’s grandfather was in charge, it knows how to fight for its life. It can take Brexit. What it can’t take is Mr. Corbyn and Brexit.

So ends my paean to moderation — to not assuming things will go well, to a kind of watchfulness toward history. To not pushing it too far.