The S&P 500 just dropped 20% in a month. Walk me through how this specifically impacts the bottom line of a traditional long-only asset manager compared to a sell-side trading desk.

标普500指数在一个月内暴跌了20%。请推演一下，这会对只做多的传统资管公司和投行的卖方交易台的利润底线分别产生怎样的影响？