A wave of selling hit the stock and bond markets. Although on most days that system didn't trade at all, it was unlucky enough to be in a long position that morning. Other kinds of surprise situations that can cause unpredicted losses are freezes, floods, droughts, government currency interventions and crop reports. With attention and foresight a trader can sidestep these risky situations. Another thing to understand about risk in trading is that you cannot avoid losses by careful planning or brilliant strategy.
Numerous losses are part of the process.
Any trade, no matter how well thought out, has a chance of becoming a loser. Many people think the best traders don't lose any money and have only winning trades. This is absolutely not true. The best traders lose a lot of money, but they eventually make even more over time. There is no point trading commodities if you cannot handle the psychological discomfort of making losing trades.