What are some notable blunders in history that resulted in huge loss?

Humans descending from the trees was pretty disastrous for all involved.

In the beginning the Universe was created. This has made many people very angry and has been widely regarded as a bad move.

I’d say the biggest blunder was probably the Romans allowing themselves to be encircled at the battle of cannae. Can’t let yourself be flanked. That’s like 2nd millennia BCE shit.

The Democratic National Committee decided to sabotage Bernie Sander’s candidacy.

Pharmaceutical companies were given leave to perform their own safety studies and to advertise directly to consumers

NASA thought that warnings about O rings from it engineers were overblown and sensationalistic.

The assassination of Archduke Franz Ferdinand

The Recording Industry Ass. Of America sued 35,000 of its customers.

The Warner Brothers thought George Lucas’s idea for a space movie was a crock of shit

People used to believe Il vaticano wasn't a real move

Cadbury replaced quality ingredients in their chocolate with palm oil.

Ke2

Coca Cola attempted to sell soda without artificial colouring.

The Wachovski sisters decided to make a 4th Matrix movie.

Steve Balmer said the iPhone would go nowhere.

Trump said COVID would vanish in 2 weeks