When someone is optimistic about the trading commodity he is interested in, such as Bitcoin, then he is considered a bull. He will want to buy. Many bulls together will want to buy and this moves the price in an upward direction.

Conversely, when someone is pessimistic, he thinks the prices will go down or perhaps has come close to reaching its potential and should start coming down. This person will want to sell. Or he may even choose to short the commodity. Enough bears will move the price in a downward direction.

A person can change from optimistic to pessimistic or vice versa very quickly. Perhaps at $200 he felt it was a good time to buy but the market has been moving upwards for a while and now at $225 he is starting to think that it's been too long and something is bound to change soon. It's kind of like that feeling you get when approaching an intersection and you've watched the light remain green for the past 10 blocks as you've approached. You start to get this feeling that it's going to turn red before you get there because it's been green too long. Sometimes you're right and you feel all smart in how you "predicted" this and other times you're surprised when you breeze right through the intersection. Anyhow, at any given time there are always bulls and bears present. When the bulls outnumber the bears this is considered a bull market and the price will start to rise, opposite when the bears outnumber the bulls.

There is an old saying: The bull goes up the stairs, the bear goes out the window. People move forward and invest cautiously but they spook very easily and sell out very quickly. This will drive the price down much faster than it went up.

Back to what I was saying in the original post, a person who is either a bull or a bear is interested in the market but feels the time is right now to either buy or sell. This is not the same thing as all the Bitcoin haters who come on here just to tell other people how stupid it is and how it can never succeed and has no intention of ever getting into the market at any point. This person just wants Bitcoin to crash to vindicate his indecision and not getting involved in the first place, AKA a coward.