IS curve a unicorn?

Could it really be possible that the IS curve, a fundamental concept in macroeconomics used to illustrate the relationship between interest rates and the output of goods and services, is actually a mythical creature akin to a unicorn? Surely, this concept, which represents the equilibrium of the economy's investment and savings at various levels of income, is a well-established and essential tool for economists to understand and analyze the behavior of an economy. Is it not a bit far-fetched to equate such a fundamental and widely accepted economic concept with a legendary creature known for its rarity and elusive nature? Surely, the IS curve is a well-documented and empirically tested tool, not a unicorn.