The Godfather, Don Vito Corleone was meeting with Virgil Sollozzo at his Genco company, along with his two eldest sons, his Consiglieri Tom Hagen, and his two Caporegimes. The Godfather listens to Sollozzo’s proposal about drugs, and then gives Sollozzo his final answer: "No!”

In the end, the Corleone Family wound up going along with Sollozzo’s original deal, minus Sollozzo. If The Godfather had said "Yes!”, the following would not have occurred:

01: There would have been no great War of 1946
02: Don Vito Corleone would not have been shot
03: Sonny Corleone would not have been killed as a result of that war
03: Michael would not have been punched by Capt. McCluskey, the result being a broken and disfiguring jaw
04: Michael would not have had to kill Sollozzo and Capt. McCluskey
05: Michael would not have been exiled to Sicily
06: Appollina would not have been killed (nor Calo, in the novel)
07: Michael would not have become the future Don
08: Carlo Rizzi would still be alive (or dead, if Sonny wound up going too far to teach the sum-bitch a lesson)
09: Tessio would not have betrayed the Family and would still be alive

Destiny is a fragile thing. One simple No or Yes answer can change the outcome in a major, complicated way. Yet, in neither the book nor the movie, nobody observed this fault of Vito Corleone. The Family got involved in the drug deal anyway, but the fallout of his initial No changed so many things.

You do know this is fiction, right?

it still would have happened because they needed to make the movie

If Peter Parker never got bitten by that radioactive spider:

THERE WOULD BE NO SPIDER-MAN FRANCHISE.

I think 7 to 9 would still have come to pass.

If that first R2 unit wouldn't have broke:

Luke would still be on Tatooine, whining about how his uncle never let him join the academy

I've got to much time on my hands....

Come on you know the Styxx song sing it with me!!

You can say that about any plot point near the beginning of any film. If so-and-so never happened, then all the shit after it wouldn't have happened. How is this a big discovery?

Domo arigato, Mr. Roboto?

If R2 had not run off to find Obi-Wan, Luke would never have left the farm and he would have been there when the stormtroopers came. He would have been killed along with his aunt and uncle. The rebellion would have been crushed without Luke. The Emperor would have ruled forever. R2 is the true hero of Star Wars.

If the Star Destroyer gunner had just done his job and destroyed the escape pod, they'd never have had to worry about any of it.