John Pemberton was stabbed in the chest during the Civil War and, to quell the pain, he became addicted to opium which then prompted him to seek out alternative drugs.
Without many options, he began to screw around with coca, kola nuts, wine and other ingredients. He patented the product and sold it as a medicine called "French Wine Coca" but then was required to drop the alcohol from the mix, prompting him to rebrand the drink as a common beverage. He then gave it the more puritan friendly name, "Coca-Cola".
Another example of a butterfly effect is that of a Reddit user, 2354PK, "I ended up sitting next to a woman who was a bit older than me on the metro home while living abroad in Paris. She took one look and asked me what was wrong, as I seemed upset. I then word vomited out how stressed I was over school and that was lonely as I was having a hard time making friends with the other kids in my program. She proceeded to tell me she was meeting up with a few of her girlfriends and I should come along.
"One of those friends was a younger sister of one of her good friends, about the same age as me, and we ended up hitting it off. She became my best friend almost instantly. Three weeks later, she invited me to dinner with her best guy friend and we also became friends. A few weeks after that, I got invited to hang out with a few people that were in their law program at said guy friend's apartment, wherein I got drunk as hell and ended up sleeping it off in his room, only to realise that I had a crush on him while lying in his bed the next morning.
"We started dating maybe a week later and were inseparable until I had to go home to the US – after that realised I needed to be with him. I moved back as soon as I could legally, and got married shortly after to start the immigration process.
"So, because some random 30-something woman broke the standard protocol of ignoring everyone on public transport to ask why I looked sad on the Paris metro a decade ago, I now have a husband, a baby, and a life in France."
See the video below for more extraordinary examples of the butterfly effect.