This article shows two examples of how the symmetrical formation recently proved itself as a reliable technical formation.
Here is the daily soybean chart that formed a symmetrical triangle that was breached to the upside. You can see that after the market broke higher out of the triangle it then trended higher for another 30 cents/bushel and could still move higher yet. However, it doesn't need to in order to prove its reliability to me as a great technical formation.
Daily March soybean chart
On the daily gold chart below we see the see the symmetrical triangle work in the opposite fashion to the downside. As the bottom of the triangle was breeched lower we then saw gold prices fall another $56/ounce or so and it's still trending lower as it continues to take out new areas of support. Again gold does not need to fall further in order for the symmetrical triangle to prove it's reliability.
Daily April gold chart