bear markets are usually easy to identify because they're usually precipitous. People investing in this stuff are trying to make quick returns, and when that's not happening they start to pull out and try elsewhere. When the price starts to dip significantly, people panic and sell, causing a vicious cycle that exacerbates the drop. Knowing this will happen, people NOT panicking also sell hoping to buy in at a lower price, further exacerbating the drop.

Once only masochistic holders like myself are the only ones who haven't sold off, the drop will stop, and once it's stopped people start to flood back in looking for quick returns.

(http://www.autoadmit.com/thread.php?thread_id=3924573&forum_id=7#35652640)