The Theory of Narrative Causality aside, there are many things that are NOT probable. Green Rocks and Applied Phlebotinum often shift the scales, but seldom the odds - the odds shift themselves. To word this better, once a thing has happened, it is much easier for it to be done again. Similiar to a mantra in Discworld; once things have happened, they have a tendency to happen again. The probability of an event increases slowly but steadily, until Rocks Fall, Everyone Dies or it approaches 1. Compare So Last Season. Applied to defeating villains, heroes, and attacks, this trope leads to Villain Decay, The Worf Effect, and The Worf Barrage.
Examples:Anime and Manga
- In Dragon Ball Z, the legendary Super Saiyan transformation was seen as impossible to achieve, yet so powerful and dangerous that it merited the destruction of the Saiyan homeworld and the near-genocide of their race. It took Goku, who was prophesied to get it, amazing emotional and physical stress to achieve it. Ditto for Future!Trunks, Vegeta, and Gohan. Then they discovered that there are levels to the Super Saiyan transformation. Then Chibi!Trunks and Goten, Vegeta and Goku's pre teen children, discovered they could transform at will, just because. And then they discovered that the key to the truly legendary transformation (the one that warranted the genocide in the first place) were the Saiyan tails that Goku and Vegeta had long since gotten removed as liabilities.
- In the Discworld novel Monstrous Regiment, the main character is a woman. However, it is gradually revealed that apparently so is everyone else in her squad, with the exception of the nebbishy lieutenant, and including the extremely auspicious Sergeant Jackrum and a third of the high command.
- The Ellimist Chronicles establishes that while the odds against the Ellimist's ascension were tremendous, the odds of it happening a second time, to Crayak, were very good.
- This is a game mechanic in Ancient Domains of Mystery. Items that you've found once are slightly more likely to be generated in the future. This is partly to make it so that spellcasters can actually use their spells without worrying about permanently running out of their good spells before finding a new book.
- In Resonance of Fate, Bonus Shots work like this. If you attack an airborne enemy, you might get to roll the Bonus Shot chance, and your ability to succeed on the second shot goes up with every bullet you hit any airborne enemy with, stacking until the end of the fight or until you actually make a Bonus Shot. Also, after you actually make a Bonus Shot, well... your enemy's already in the air, so if you've still got actions left, just keep shooting and start building your chances up again.