ANSWER:

From personal experience, the reverse is more common. Symmetricals are so time-consuming (relatively speaking) that it is nearly impossible for a market to hesitate long enough to complete the entire pattern during one, sideways period. As a result, Symmetricals tend to have a decided upward or downward bias. Initially, their “trendy” nature can make them difficult to identify. But, after a Symmetrical passes its halfway point, the extreme price/time similarities between all “same direction” waves makes it easy to determine one is forming.