A slightly off-topic question. I wasn't trading (or watching the markets) in the months coming up to the top in 2000, but I hear that no one dared short/call the top. So, when it came, it just cascaded. Here's what I'm getting at, since then (in this bull market), everyone remembers what happened in 2000 and so are very wary of the rallies; as a result they call tops/build short positions in a healthy rally. Could this be contributing to the length of this bull market (pleany of people shorting/trying to catch a top and then covering after taking a hit)? If this is the case, what's to keep us from continuing up?