9. 300 - Disregarding The Hunchback Ephialtes
Heavily stylised and massively successful, Zak Snyder's 300 was the film that catapulted the director into blockbuster success. It's based on the famous Battle of Thermopylae in which the titular Spartans managed to fend off an entire army of Persian invaders for three days. This power is always on display throughout the movie.
Outside of some losses to the Persian Warrior Elite, the Spartans seem nearly invincible; they're able to best countless waves of soldiers and even the mightiest war elephants. But there's one flaw in Leonidas's plan; a deformed hermit he refuses to acknowledge.
Ephialtes betrayed the Spartans and assisted the Persians in their victory at Themopylae. In the film, he is a hunchback who wishes to reclaim his family's lost honour by fighting with the 300. While Leonidas is sympathetic towards him, he refuses Ephialtes a place, feeling his inability to raise a shield would compromise their battle formation.
This proves to be the leader's undoing as the embittered outcast heads over to the opposing side, revealing a hidden passage that allows Xerxes to flank the warriors from behind. Had the Spartan King allowed Ephialtes into his ranks, he would have avoided this betrayal. As it stands, this decision leads to the Spartans' eventual defeat.