Howard Marks: A true bubble requires investors to be completely unaware and usually meets several conditions at the same time: Market valuations are clearly detached from rational investor judgment Risk appetite is severely out of touch with reality Investor sentiment is completely out of control Valuation data supports this judgment: The current forward P/E ratio of the top five tech stocks is about 23x, far lower than the 65x at the peak in 2000. Precisely because everyone is talking about a bubble, it means the bubble is still far from bursting.