The Sages do not invent law from nothing. They derive it from verses — but the derivation is rarely the surface meaning of the verse, and almost never the only possible reading. This essay takes a single verse from parashas Mishpatim and follows its journey through the Talmud, showing how a binding halacha is produced.
The point is not the specific halacha. The point is the method: how the Sages decide, when a verse permits more than one reading, which reading the law follows.