The good folks at TickerSense have a harrowing post up about how one analyst utterly missed it as monoline insurer Ambac fell 93% over the last year. Harrowing reading.
As shown, the analyst maintained a "Buy" rating on the stock throughout the 90% decline. Throughout the decline the price target was reduced from $103 to $18 (-82.5%), and yet the "Buy" rating was maintained. The stock was downgraded to "Hold" on 1/18, at the low close.
Read it and weep.