No matter how bad you think you messed things up at work you can always take heart in the fact that in 1788 the Austrian army attacked itself and killed 10,000 of its own men. These are the 25 biggest and most embarrassing mistakes ever made.
NASA accidentally taping over the moonlanding. In fact, there are no known original recordings of the event.

It took 177 years to build the Tower of Pisa and only 10 years for it to start leaning

Not having enough life boats on the Titanic because it was "unsinkable"

Decca Records turning down the Beatles because they weren't sellable. Enter EMI.

NASA loses a Mars orbiter because part of the team used metric units and the other half used English.

Napoleon thinking he could invade Russia in winter

Hitler thinking he could do any better than Napoleon

The Persians sending Genghis Khan's ambassador back to Genghis Khan without a head and bringing the wrath of Mongolia down on themselves

The Dutch discovering Australia 100 years before the British but ignoring it because they thought it was a useless desert

Russia selling Alaska to the US for 2 cents an acre because they thought it was a useless tundra

Inca ruler Atahualpa agreeing to meet Conquistador Fransisco Pizarro during which 200 Spanish horseman ambushed and defeated 80,000 Inca warriors

Although no one is sure whether or not the Trojan Horse actually existed, if it did, it was worthy of this list

Filling the Hindenburg with hydrogen

Somebody leaving a gate open and allowing the Turks to sack Constantinople in 1453

14th century China abandoning its navy and pursuing a policy of isolationism. It arguably could have been much more influential than any European power.

Archduke Franz Ferdinand's driver making a wrong turn that led right to the feet of his assassin, Gavrilo Princip. Two World Wars that could have been at least postponed by a Garmin.

The Japanese attacking Pearl Harbor when not a single US aircraft carrier was in port

Faulty construction leading to the meltdown of the Chernobyl Reactor, the consequences of which are still being counted to this day

The 12 book publishers that rejected Harry Potter

Alexander the Great not naming an heir which led directly to the fall of his empire

Not giving Hannibal siege equipment, which lead to Hannibal basically ignoring Rome, which led to Rome basically destroying Hannibal

Although nobody knows who was responsible, the burning of the library of Alexandria was potentially the world's single greatest loss of knowledge ever

Thinking that the West Indies was Southeast Asia

Assassinating Caesar in order to save the Republic and not realizing that the assassination would all but ensure its demise

In 1788 the Austrian army accidentally attacked itself and lost 10,000 men
