Positive emotions could cause us to fail to apply risk precautions. Negative emotion could cause us to hesitate. Trading is a psychological game. Most people think that they're playing against the market, but the market doesn't care. You're really playing against yourself.
Losses are a simple cost of doing business.
Don't try to justify a bad trade by convincing yourself that it will sooner or later turn into a good trade. Successful traders are able to ride through periods of drawdown. The confidence in their methods reassures them about their future success. The markets offer endless and plentiful possibilities. Missed opportunities exist only in your mind.