Characters and stories are known for building their internal conventions, be it a Catch Phrase or Running Gag, it is often introduced as something they have been doing for a long time. This is when time is taken to actually explain where that specific convention came about, be it through a Flashback, Prequel or merely a story told through dialogue. Examples:
- In Home Improvement, the quirky neighbor Wilson would great Tim with "Hidey-Ho Neighbor" and it was just his Catch Phrase. Wilson decided to put on a stage performance detailing the interesting things he had done in his life, he brought up an encounter with an African Tribal leader who greated him in his native language, which translated out to "Hidey-Ho Neighbor." Tim and family exclaimed "That's where it comes from!"
- Al was known for always wearing flannel and was sometimes teased about it. In a male bonding session Tim learned that it is because Al's father would give him a flannel shirt to wear when working outside.
- The Big Bang Theory episode "The Staircase Implimentation" was a flashback to when Leonard first moved in with Sheldon. It featured several nods to their current habits including Sheldon finding "his spot" on the couch. And a running set piece the show uses is the characters having to climb the stairs of their apartment because the elevator was out, and Leonard explained the story of how it got broken in the first place. Leonard tried showing off some experimental rocket fuel to Howard and Raj, only to get the mixture wrong. In an attempt to get it out of the building Sheldon forced Leonard to leave the elevator with the canister inside, exploding and destroying the elevator.
- Scrubs has used this a few times with explaining the characters personality quirks, most of them issues with their parents. Elliot has a hard time using proper terminology for sex organs because her mother would use those same terms and sneak away with the pool boy. Todd is a lecherous Casanova Wannabe because his father acted the same way.
- While not quite explaining the origin, J.D. and Turk's affectionate nickname of "Chocolate Bear" and "Vanilla Bear" for each other came about in college when they had a third friend, a Hispanic guy named Ricky who went by "Caramel Bear."
- Burn Notice has Sam frequently using the cover-ID of Chuck Finley, tying himself to that name fairly tightly, "Chuck Finley is forever." In the prequel movie Burn Notice: The Fall of Sam Axe it shows him using that name for the first time, taken from the cover of a sports magazine (Sam is not a trained spy but a special forces operative, that was his first time taking on a cover).
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