Not all write-downs are created equal. That's a lesson being personally and painfully learned during this season of reckoning on Wall Street, as big banks are taking king-size hits against earnings because of losses on mortgage-backed securities, structured debt products and loans backing leveraged buyouts. Already the damage has helped claim the jobs of two CEOs -- Merrill Lynch & Co.'s Stan O'Neal and Citigroup's Charles Prince. Looking at the size of these write-downs as a percentage of the firms' market capitalization, however, provides some interesting context. Financial titans like Bank of America and JPMorgan Chase & Co. are big enough that their third-quarter losses were less than 1 percent of their market values. But for smaller, less diversified firms that took risks on par with their bigger rivals, the outcome looks far worse. Merrill's $8.37 billion write-down, for instance, represented more than 11 percent of its market cap.