We're seeing the same setup in shares of Panera Bread ( PNRA) right now. Like Foot Locker, mid-cap Panera is forming a descending triangle -- in this case with support at $155. The sell signal comes when shares slip below the $155 level that's acted like a price floor for shares for the past several months. Whenever you're looking at any technical price pattern, it's critical to think in terms of buyers and sellers. Triangles, rectangles, and other pattern names are a good quick way to explain what's going on in this stock, but they're not the reason it's tradable. Instead, it all comes down to supply and demand for shares. That support line at $155 is a price where there's an excess of demand of shares; in other words, it's a place where buyers have been more eager to step in and buy shares at a lower price than than sellers have been to sell. That's what makes the breakdown below $155 so significant -- the move indicates that sellers are finally strong enough to absorb all of the excess demand above that price level. That's when you want to sell -- or short -- shares when it happens.