If you hold shares of one of Japan???s three biggest banks — Mizuho Financial Group (MHFG), Mitsubishi UFJ Financial Group Inc. (MTU) or Sumimoto Mitsui Financial Group Inc. (SMFG) — it might be time to loosen your grip on those companies??? stocks. Each significantly underperformed annual earnings estimates for 2013. Mizuho admitted that net income may fall as much as 20 percent from the previous year. Sumimoto forecast a 19 percent drop in revenue, year over year, and Mitsubishi revealed its revenue will trail the prior year???s sales by 3.5 percent. Not surprisingly, shares of each fell after the announcement, continuing a downward trend that has been going strong since the beginning of 2013. Specifically, Sumimoto is down 25 percent year to date. Mizuho is off 11 percent, and Mitsubishi has lost 17 percent of its value this year alone. Is that enough to convince you to sell your shares?