A solitary man, José Arcadio Segundo is traumatized when he lives through the banana company's massacre of 3,000 workers. He spends the rest of his life trying to convince Macondoans that this event really took place.
One of the persistent themes of the novel is how prone history is to being forgotten. Whether it's because of the insomnia disease, or because history is written in some crazy indecipherable code, or because those old enough to remember are unable to communicate with those young enough to learn, the historical memory of Macondoans is constantly being wiped clean. You know what they say about those who forget history? That they are doomed to repeat it. And in this book, boy, do they ever.
No forgotten event is as shocking as the planned massacre of the 3,000 banana plantation workers who come to peacefully ask for better working conditions. Not only are they methodically killed, but their corpses are loaded up on trains and then dumped into the ocean. (Imagine how much manpower and time it would take to load that many dead bodies onto train cars – this is an extremely well-orchestrated massacre.)
Astoundingly, no one except José Arcadio Segundo – who was there in person and somehow managed to survive – believes this event took place. The government puts out a big lie about how the workers got what they wanted and then went home, and everyone in the town buys it. José Arcadio Segundo is destroyed not so much even by the horrible event itself (although, really, waking up in a pile of dead bodies would be enough to throw even the hardiest man into a mental tailspin), but by his growing obsession with proving the truth of what he saw to those resistant to it.