Years. In December 1996, Fed chairman Alan Greenspan warned of 'irrational exuberance' in stock prices, yet the market kept climbing for more than three years before the dot-com bubble burst in March 2000
Greenspan's famous phrase was widely read as a caution that shares were overvalued, but prices kept soaring afterward and his warning looked premature for years. That gap is exactly why early alarms get dismissed: a warning can be correct about the danger and still be 'wrong' for a long stretch, so investors stop listening right up until the reckoning arrives.
