An economic bubble (also called a speculative bubble or a financial bubble) is a period when current asset prices greatly exceed their intrinsic valuation, being the valuation that the underlying long-term fundamentals justify. Bubbles can be caused by overly optimistic projections about the scale and sustainability of growth (e.g. dot-com bubble), and/or by the belief that intrinsic valuation is no longer relevant when making an investment (e.g. Tulip mania). They have appeared in most asset classes, including equities (e.g. Roaring Twenties), commodities (e.g. Uranium bubble), real estate (e.g. 2000s US housing bubble), and even esoteric assets (e.g. Cryptocurrency bubble). Bubbles usually form as a result of either excess liquidity in markets, and/or changed investor psychology. Large multi-asset bubbles (e.g. 1980s Japanese asset bubble and the 2020–21 Everything bubble), are attributed to central banking liquidity (e.g. overuse of the Fed put).
In the early stages of a bubble, many investors do not recognise the bubble for what it is. People notice the prices are going up and often think it is justified. Therefore bubbles are often conclusively identified only in retrospect, after the bubble has already popped and prices have crashed.

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