Not all mistakes deal the same level of impact. Some mistakes that might even seem minor enough at their onset will only end up going on to unleash all kinds of unwanted havoc. This is why it’s especially crucial to do what you can to remain vigilant and present as you go about engaging with life on a daily basis. With that being said, don’t be too hard on yourself at the same time. There’s a balance to everything.
1. Alexander Fleming and the petri dish.
“I’d like to cast my vote on Alexander Fleming forgetting to put the lid on his Petri dish, discovering penicillin thanks to it. Saved millions of lives by a mistake.” – u/NoveltyEducation
2. The open borders incident in Germany.
“The guy who announced on a press conference that the borders between the divided Germany are open, starting right now, which was basically a series of misunderstandings/miscommunications. This ultimately lead to the fall of the Berlin wall, the reunification of Germany and arguably to the collapse of the Soviet Union.” – u/Joncas93
3. The missing binoculars that sunk The Titanic.
Michel Boutefeu/Stringer/Getty
“David Blair (the intended second officer on the Titanic, who was replaced before the voyage) forgetting to give the replacing crewman the key for the locker containing the binoculars. As a result, the night watchman couldn’t see as far, and only noticed the iceberg by the time it was too late.” – u/Captain_Kruch
4. Laying waste to the Alexandrian library.
“Burning of the Alexandrian library. Caused a massive loss of collective history, knowledge, arts, crafts, architecture, politics, language, social structuring.” – u/_Independent_1177
5. Lead and gasoline.
Putting lead in gasoline was one of the biggest public health mistakes of the 20th century. While tetraethyl lead helped reduce engine knocking and improve fuel efficiency, it also released toxic lead particles into the air, poisoning millions. Lead exposure is linked to neurological damage, reduced IQ, and increased aggression, especially in children.
The widespread use of leaded gasoline contributed to higher crime rates, environmental contamination, and long-term health crises before its phase-out began in the 1970s. The damage was preventable—scientists warned about lead’s dangers from the start—but corporate interests and profit motives delayed action for decades.
6. The forever chemical.
“DuPont and Chemours and their forever chemical PFOA and other PFAS. PFOA, a forever chemical, is estimated to be in the bloodstream of 99% of all humans on earth. It’s probably the same for animals, too. Cancers, birth defects, etc., all could be caused by this. The worst part is, chemical companies knew about it as back as 1950 yet continued to manufacture it.” – u/deleted
7. Distilled ammonium.
Using distilled ammonium in fertilizer was a massive mistake because it directly contributed to environmental destruction and global instability. While it helped boost crop yields, making modern industrial agriculture possible, it also led to massive nitrate pollution in waterways, creating toxic dead zones in oceans and lakes—excess ammonium fertilizer seeps into groundwater, contaminating drinking water and posing health risks.
Worse, it’s a key ingredient in explosive materials, fueling conflicts and terrorism worldwide. The push for ever-higher yields at any cost has led to soil degradation and a cycle of dependency, making agriculture more fragile rather than more sustainable.
8. The gold standard collapse.
“When the gold standard collapsed in 1914.” – u/Solid_Buy_214
9. Chestnut Blight fungus.
“The accidental introduction of Chestnut Blight fungus to North America. The fungus came in on Chinese Chestnuts being planted at the Bronx Botanical garden in 1904. It quickly escaped and it only took 30 years for that fungus to almost completely eradicate the American Chestnut throughout all of Eastern North America.” – u/Nor_easter23
10. Franz Ferdinand’s driver.
Franz Ferdinand’s driver made one of history’s most consequential wrong turns. On June 28, 1914, after an earlier failed assassination attempt, the Archduke’s motorcade mistakenly turned onto a side street in Sarajevo—right where Gavrilo Princip happened to be standing.
The error put the heir to the Austro-Hungarian throne directly in front of the assassin, who seized the moment and fired the shots that changed the world. That small navigational mistake set off a chain reaction of events that led to World War I, the collapse of empires, and the geopolitical reshaping of the 20th century.
11. Mao’s Great Leap Forward.
“Mao’s Great Leap Forward, which ultimately led to death by starvation of millions, maybe tens of millions; and set things up for the Cultural Revolution.” – u/LAWriter2020
12. Sega Saturn messing with its release date.
“Sega Saturn’s release date was moved up in an attempt to get a head start on the fall season, before the highly anticipated PlayStation was to debut. It backfired.” – u/theycallmemomo
13. The misuse of the Aeolipile engine.
“That the Aeolipile engine was not put to better use, we could have had the industrial revolution almost 2000 years early, and we could be sailing the stars by now.” – u/eyeeyecaptain
14. The whole climate change debacle.
“It’s probably too early to say for sure, but the failure to address climate change is very likely to top the list 100 years from now.” – u/colanolberding
15. No love for Nikola Tesla.
“Not fully funding Nikola Tesla.” – u/_Tesla01
16. Dismantling North America’s streetcar and passenger rail systems.
“Hard to settle on the biggest one, but in terms of mistakes having lasting negative effects on the world, I’d point to the dismantling of North America’s streetcar and passenger rail systems in favor of automobile-centric development and airplanes, which ruined cities and is a major contributor to climate change.” – u/availablefield102
17. The origins of the mortgage crisis.
“Barney Frank’s election to the House and subsequent blocking of attempts by both the Clinton and Bush administrations to re-regulate Fannie Mae and Freddie Mac led directly to the subprime mortgage crisis and the economic collapse in 2007-2008.” – u/jack_daone
