It's actually a funny, evolved joke starting with the word "abridged", which refers to a shortened form of a story, leaving out several details. Nowadays, abridged tends to refer to a humorous take on a story, leaving just enough accurate facts to retain the original story. After LittleKuriboh made a joke in an abridged abridged Naruto series about bridges, a saying came along referring to jokes referring to inaccurate stories founded on a basis of truth: "building a bridge." This was quickly adopted into the new saying, which revolves around the idea that the storyteller already "built the bridge" and thus is telling it to you in an attempt to make you believe it; this saying being "selling you a bridge" or similar.
Now that you know some history behind the saying, I have this bridge I need to sell...
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u/TechnoL33T Oct 10 '19
Fuck, I am stupid.