We Only Have One Chance

The odds are down, the enemy's tied the heroic group to a chair and have a nuclear missile pointed straight at them. All's lost, right? Wait! There's a Million-to-One Chance that they can get out of this situation victorious, but it will take split second timing. Of course, instead of attempting to do this split second timing, the heroes point it out to each other that the chances are minimal through the phrase:

"We only have one chance!"

Which, of course, means they'll invariably succeed. May be used in situations where It Only Works Once.

Examples of We Only Have One Chance include:

Anime

In Code Geass, Suzaku used his "Live on!" Geass to perfectly time his attack, which allowed him to exploit the One Chance he had to deactivate FLEIJA.

Web Original

Yugi says this in Yu-Gi-Oh!: The Abridged Series. Ironically, it doesn't work.

Western Animation

Superfriends was the embodiment of this trope. Every episode, one or all of the heroes would get into a deathtrap situation where their only means of escape involved extremely unlikely scenarios, shady impossible physics, developing a new super power spontaneously, or often all three. Of course, they'd never fail to say "I only have one chance" before executing their bold strategy.
In The Incredibles, Elastigirl mentions that they'll only have one shot at defeating the Omnidroid by blasting its claw through its core. To improve the chances, she makes Mr Incredible wait until the last possible moment to take the shot, so the Omnidroid is closer.
The Real Ghostbusters is MADE of this trope. Expect Egon to say it at least once an episode.
The Fox and The Hound

Todd: Quick, Vixie, this is our only chance!