Observation from a long time (retired successful) trader:

""working hypothesis" about an end of qtr. portfolio blowout from institutional fund managers. Per se:

2 wks of upside takes the market thru the 1st wk for February. 3 takes it to mid month. In the final week, the primary down trend resumes. With a vengeance as we get into March.

Pressure quickly builds on fund mgrs to get out of their weakest holdings before "the picture is taken" (i.e.having to list their portfolio positions for the quarterly report to fund shareholders.

Once that happens? Tape starts showing more and more big blocks (10, 20, 30k shs., or more) going across on down ticks. The selling soon feeds on itself. No mgr who values his job wants to be the last one outta the weak - YTD - stocks. Next, margin are generated among leveraged players? And you get a classic washout low to buy into."