There is a huge difference between trading and investing Lara, investors like to group together and talk about the comapny to the death. A trader sees a stock with short term potential and trades it and get's on to the next trade.
The stock market is an evil place, i have seen people lose their homes, wife and kids through being made bankrupt. Only the other week a poster was talking about taking his own life through losses he had made hoping to trade a few points and he has not been the first and won't be the last.
A stop-loss is one of your must have rules, along with funds in the bank to cover.