Brexit. As historical blunders go, this has a beautiful unambiguous purity.

Twitter

We’ll there was that time Kublai Khan tried to invade Japan with the largest amphibious assault in history (until D-day) and got absolutely wrecked by a typhoon.

Then tried again a few years later, with an even larger force, and got wrecked by another typhoon.

https://en.wikipedia.org/wiki/Mongol_invasions_of_Japan

World War I didn't do anyone any good whatsoever; including any of the various parties that might be blamed for starting it.

Napoleon's invasion of Russia. It led what might be the first great infographic ever though. Charles Minard’s Infographic of Napoleon’s Invasion of Russia from 1869 (Carte figurative des pertes successives en hommes de l’Armée française dans la campagne de Russie en 1812-1813)

Tan colour line from left to right is the trip from France to Moscow, 1mm line weight = 6000 soldiers, black colour line from right to left is the trip back to France. The line slowly thins and diverges like a tree branch until 422k soldiers are whittled down to 10k returning. Not quite the outcome Napoleon had intended.

When the Spanish were raping the New World in the 1500s for gold, they dumped enormous quantities of platinum into the ocean because it was the wrong kind of shiny metal. Nobody in Europe had any clue how valuable the stuff was, only that it was often used to counterfeit gold. But since it wasn't gold, or even silver, everyone thought it was worthless. This was exasperated by the fact that nobody could melt the stuff until the 1800s. But mostly it was just not yellow enough for the idiots at the time.

King Pyrrhus of Epirus. He was known for winning battles against superior armies, at the cost of taking heavy losses. He was once quoted as saying "If we are victorious in one more battle with the Romans, we shall be utterly ruined."

He was so famous for this, that the term for a victory that devastates the victor bears his name, a Pyrrhic victory.

Knight Capital - They were biggest equities trader in 2012. They manually deployed code and didn't get configuration right and it reactivated "Powder Peg". They lost $460 M in 45 minutes and went bankrupt.

The Jan. 6th insurrectionists who thought Trump was going to pardon them all because they were heroes.

Buying Twitter for 44B and renaming it to X.

Since December 1982, the O-rings had been designated a “Criticality 1″ item by NASA, denoting a component without a backup, whose failure would result in the loss of the shuttle and its crew.

Richard Feynman[:] “… [the shuttle] flies [with O-ring erosion] and nothing happens. Then it is suggested, therefore, that the risk is no longer so high for the next flights. We can lower our standards a little bit because we got away with it last time. You got away with it, but it shouldn’t be done over and over again like that.”

Taken from an excellent writeup of the fatal 1986 Challenger flight.

Russia invasion of Ukraine. They used to be number 2 army with sophisticated weapons. Now they are number 1 world laughing stock with weapons that works exceptionally well for invading Mars but not on earth.

Elon acquiring Twitter for $44B in the first place, not taking into account the subsequent blunders. He not only overpaid too much for a social media company without even understanding it, he also wrecked Tesla's stock price as investors saw he was clearly spending too much time on Twitter and he had to panic sell Tesla shares to fund his Twitter adventure. He easily wiped out hundreds of billions from Tesla's market cap during that time.

The Gunpowder Plot. Guy Fawkes and his friends were about to blow up parliament, and on the week it was supposed to happen, one of his accomplices sent a letter to a noble. In what was probably the worst example of "asking for a friend" in history, it asked "hypothetically, what would happen if someone went into the basement and blew up parliament". The noble did what nobody expected he would do and, get this, responded to the letter. People searched the palace basement and found Guy Fawkes, he was arrested and killed, and we have Guy Fawkes Day. The reason this led to a loss is because the king of England at the time used it as an excuse to persecute Catholics and make the holiday which is used as a taunt.

Chernobyl comes to mind as the biggest fuck up ever. Whenever I think I fucked up I try to remember, it can never be as bad as Chernobyl.

Didn't really result in a loss, but a huge missed opportunity, when AT&T turned down an offer for them to purchase the early internet.

I'm willing to nominate Charles II, King of Spain as a formerly alive blunder. The result of decades of Hapsburg inbreeding, he had a number of health and intellectual issues from birth and he was notably infertile. If you live in a monarchy where succession is passed down through children, it's REALLY BAD to be infertile and be King. His death directly caused the War of the Spanish Succession, a 13-and-a-half year war that eventually involved pretty much all of western Europe and likely led to the deaths of over 1 million people.

Literally could have avoided this if the Habsburgs decided to have sex with other people.

Target's failed expansion into Canada. It's taught as a case study on what not to do in business schools now.

In terms of money and business, my fav is how Xerox didn't know how to market/capitalize on what was effectively the first personal computer before personal computers were even a concept, which is estimated to be a $1.4 trillion mistake.

Long-Term Capital Management was a hedge fund founded in 1994 that had notable academics and Nobel Prize winners on its board. It was very successful in the early years (while critics warned of the risks) and eventually collapsed in 1998, losing $4.6 billion in a matter of months due to its leverage and impacts of currency crises. The US government stepped in to shore up the financial system. It's taught as a case study in how a strategy can post impressive returns but quickly turn into a wipeout.

Coming down from the trees was a pretty big blunder. Nothing but losses ever since.

The first thing that came to mind, oddly enough, was Blockbuster refusing to buy Netflix for the equivalent of a rat and a string to swing it with.

Scotland trying to colonize the Darien gap It bankrupted Scotland and forced the union of England and Scotland to be the UK.

The Battle of Manzikert led directly to the end of the Roman Empire, all because of mismanagement.

Pretty much anything the government in my country does results in a huge loss of state funds lol

Cambium stock recently dropped to $10 after the CEO stepped down during their call. A large part of their problems are likely due to the pandemic shortages catching up.

But a high failure rate on their new line of switches, and high prices while starlink eats their lunch isn't helping.

Edit: Used to be over $50.