When we experience a period of failure, we become pessimists. In fact, a trader should worry about a loss only if he was trading against the trend or breaking the rules of his trading system. Professionals that loses are not a big problem, and it happens regularly. There is no reason to start being upset if you lost some money, but at the same time did everything right, were disciplined, and did not do stupid things. But on the other hand, there is no reason to love losses or to treat them indifferently. Your reaction to losses is a reflection of how you received these losses, how accurately the rules of the trading system were followed. Loss line is a signal that a trader is doing something wrong. It is a signal that you need to move away from the market for a while.
If you start being pessimistic, then you fall into the trap of the past, your present is destroyed, and the future disappears. One failure with uncontrolled pessimism can lead to a destructive streak. Losses are an integral part of trading, and one of the main differences between successful traders and the rest is not how much loss they have, but how they deal with these losses. The ability to lose is the key to being a winner in the long run. The calmer you endure failure, the more profitable your trade will be.