Han Solo's Broken Stick
The Star Wars story, written by the great George Lucas, is full of cause and effect events. One such event appears so minor it is often overlooked as a pivotal moment, yet I believe this event carries the future of the Rebel Alliance.
In Star Wars Episode VI, Return of the Jedi, Han Solo leads a squad of commandos to the surface of the planet Endor to destroy the Death Star's shield generator. As the squad moves through the forests of Endor, they come upon a group of Scout Troopers with Speeder Bikes. Han decides that he and Chewie will 'take care' of them, and the two sneak off through the brush. When Han is almost in position to subdue one of the Scout Troopers, he steps on and snaps a stick. This is the event under consideration; without this event, the entire Rebel plan falls apart.
Before you jump to argue my position, follow the chain of events.
Han snaps the stick, which alerts the Scout Troopers. Han's scuffle with the Trooper alerts another pair of Scouts in the area, who speed off through the trees to report the incursion. In an heroic moment, Luke and Leia jump aboard another speeder bike and set off in pursuit. In the course of the pursuit, Leia falls off her speeder bike and is knocked unconscious. Leia is prodded awake by an Ewok, who eventually befriends her and leads her to his village.
To summarize from here: the Ewoks and Rebels become allies. When the Rebels are captured entering the front door of the shield bunker, the Ewoks attack, causing more confusion than real damage, but enablng Han and his crew to complete their mission when they reveal the location of the bunker's back door. The Rebel fleet, overhead and in danger of annihilation, succeeds in destroying the unfinished Death Star and ending the Empire's dominance in the Galaxy. Mission accomplished.
Let us follow the likely chain of events if Han does not snap his stick at the pivotal moment.
Han and Chewie manage to subdue the Scout Troopers along their path of advance through the forest, and the commando squad continues on. As they assault the shield bunker they are captured and carted off to be tortured and killed by the Empire. The Rebel fleet, under attack around Endor, is completely destroyed. The Rebel Alliance suffers a major defeat and requires years to regroup and rebuild its forces. Mission Failed.
In short, without the broken stick, Leia never drives the speeder bike in pursuit, and she never falls off the speeder bike. She never befriends the Ewoks and persuades them to the Rebel cause. Without the Ewoks there is no surprise attack at the shield bunker, no knowledge of the back door, and no success bringing the shield down. With the shield in place, the Rebel fleet dies. Thus, the Rebel Alliance and their plans fall apart.
Han Solo's cleverness isn't quite enough to save the day. Instead, a seemingly random event leads to success. Kudos to George Lucas.