Before answering this question, let's remind ourselves of a couple of important facts of economics. When there's a lot of demand (buying) for a certain financial instrument, its price will go up. Conversely, a lot of supply (selling) leads to lower prices. Now it will be easier to grasp the origins of the nicknames bulls and bears.
Bulls attack by bending their heads and poking their opponents upwards with their horns. (So they are buyers, driving the price up.)
Bears attack by getting up on their hindlegs and striking their opponents down with their paws. (So they are sellers driving prices down.)
But what does it mean to be a bull or a bear in forex trading? When you buy EUR/USD, for instance, you're bullish with regards to the euro and at the same time your bearish on the US dollar, so you're both a bull and a bear. As long as you're not a pig, everything is fine.
Did you know that there were pigs on the forex market? Oh, yeah, there are! Pigs are known for their gluttony, and for getting slaughtered. If you're a newbie with no experience and have decided that forex trading is a quick way to get rich, we can safely conclude you're pig. No offence meant, of course! This site was created by traders; that's why we get to talk honestly like this. We would surely not have written this if we were employees in a brokerage firm. Have you read similar stuff on a broker's site? That said, most good traders have been pigs at some point at the start of their careers, and have been "slaughtered" a couple of time (they have blown up a couple of accounts). The important thing is not to repeat the same mistakes over and over again, but rather to learn from your experience and from the experience of other traders. Your motto could be: I know I am a pig, but I am constantly fighting my piggish attitude. Come to think of it, what does the following typical newbie question look like to you?
Could I possibly be lucky enough to double my account every week?
That's a typical question of a greedy pig. Luck would at best help him keep his account afloat for a couple of weeks, instead of wiping it out in a few days as would normally be the case for a greedy and impatient novice.