The end of a film needs to leave a lasting impression. It's our whole experience of the film boiled down into the last 10 minutes: the big reveal, the lasting poignant tone, the grand pay off for investing two hours of our time into staring at a little glowing screen - so it better be worthwhile.
With that in mind, it's scary to think of what we could have ended up with if a diligent scriptwriter hadn't caught some of these catastrophic endings before they ruined their respective films.
Now, obviously, scripts go through lots of stages of development before they make it to the big screen, but when you consider some of the missteps that have almost ruined films before, it's a wonder the scripts even made it past the first vetting stage. Clearly - and thankfully - the studios realised that there was enough quality up to the flash of idiocy to justify putting in a little more work.
Still, it's frightening to think that some of the most iconic movies in cinema almost sabotaged themselves at the final hurdle, beginning their lives with a draft detailing a disastrous third act that would have blockaded their entrance into cinematic Valhalla and rendered them trash...