SAN FRANCISCO -- In this era where a stock like Citigroup ( C) is swapped among traders with the same forethought given to any random Bulletin Board issue, momentum can be a strange thing.Stocks, those of the nonfinancial variety, took quite a ride on Monday, ending a four-day rally that, with each successive close higher, had given hope to the notion that market lows touched on March 6 would stand throughout 2009. As investors have died by the financial-stock sword, so too have they been living by it, before Monday: The Financial Select Sector SPDR ( XLF) exchange-traded fund, which you may remember from its drop of about 70% from last September to just more than a week ago, closed 16 cents lower to close at $8.03. Individual financial stocks were similarly volatile: Citigroup was up 26% to $2.24, JPMorgan Chase ( JPM) fell 3.2% to $22.98 and Bank of America ( BAC) was up 5.4% to $6.07. Monday's tumult comes after a week that saw the XLF run up nearly one-third, combining with regional-bank and homebuilder-stock ETFs as the only sectors that outperformed the iShares Russell 2000 ( IWM) ETF last week. Several factors have contributed to bucking up financials, and with them, the overall market, not the least of which is was an extremely oversold condition. It has been widely accepted for a week or two that a bounceback rally was coming, whether your version was a "dead cat bounce" to set up another move down or something of the more sustained variety. But one must also bow to the lift in sentiment, if not fundamental change, provided from last week's comments by the major banks related to the cryptic "profit from operations" for January and February, as well as the possible revisiting of mark-to-market accounting and the uptick rule -- all of which led to the perception that a bottom in financial stocks could be at hand.