Not having a trading plan or sticking to one

Experienced traders get into a trade with a well-defined plan. They know their exact entry and exit points, the amount of capital to be invested in the trade, and the maximum loss they are willing to take, etc. Beginner traders may be unlikely to have a trading plan in place before they commence trading. Even if they have a plan, they may be more prone to abandon it than seasoned traders if things are not going their way. Or they may reverse course altogether (for example, going short after initially buying a security because it is declining in price), only to end up getting "whipsawed."