The Consumer Staples ETF...XLP...broke important support around the $52 level and sold off about -2.7% yesterday. This level is important because it was support in April and May, and then again throughout October. Longer-term it seems to be breaking the uptrend that began in 2008. This is an important dynamic because it is rare to see such clearly defined trends over such long periods.
Trend lines aren't magical or mysterious. They are simply graphical representations of the forces of supply and demand as time passes. Prices are always doing one of three things. Going up, going down, or staying the same. A correctly drawn trend line illustrates this.