Power struggles are common on Wall Street. What seems unusual about Merrill is how crucial decision makers — Mr. Zakaria, Mr. Kim, Mr. Semerci — quickly became pariahs. (Merrill cut ties with Mr. Kim when it announced the write-down. The bank is not expected to invest in his hedge fund.) Banks should take risk, and bank chiefs are paid a lot of money to manage that risk. At Merrill, it seems, there was talk of managing risk and hope that someone was doing it. After Mr. O'Neal wrote in July that Merrill was "managing risk and market activity every day," he said: "It's what our clients pay us to do, and as you all know, we're pretty good at it."