They may be unable to admit they have made a mistake, or they look at the market on too short a timeframe. Too many traders perceive futures markets as an intuitive arena. The inability to distinguish between price fluctuations which reflect a fundamental change and those which represent an interim change often causes losses. They believe the market is too high and keep going short, this is not based on technical or fundamental analysis just their beliefs. Yet the market keeps going higher because that where it wants to or should be but the losing trader is firm on his beliefs and keeps losing.
Many traders get a fundamental case and hang onto it, even after the market technically turns.
Only believe fundamentals as long as the technical signals follow. Both must agree. These market will result in bad fills, limit moves and erratic price movements usually against your position. And stops will be blown through. By trading more than one commodity you will help limit losses and spread your risks.