Lack of discipline is a major shortcoming. Also, many traders are unable to take a loss and do it quickly. Overtrading is dangerous, and often stems from lack of planning. Trading very speculative commodities is a frequent mistake. There is a striking inability to stay with winners.
Most traders are too willing to take small profits and, therefore, miss out on big profits.
Many traders have the habit of not cutting losses fast, and getting out of winners too soon. It sounds simple, but it takes discipline to trade correctly. This is hard whether you're losing or winning. Many traders overtrade their accounts. Futures traders tend to have no discipline, no plan, and no patience.