Professional traders will also experience defeat but continue trading because they learn from the experience and don't repeat it again. Meanwhile, for beginners, there will be a special trauma and they may not trade again. That's the difference I usually observe.
Sure, someone never becomes a professional trader if he stops immediately when he lose money. He must continue and try to learn from the losses. Learning from the losses will make them to have experience and knowledge, that's make him to stronger and smarter in trading. He will grow to be an experienced trader if he survives for a long time. This is actually what the professional has done. Well, for some beginners, they will stop when they get losses because they don't understand it well. And they mustn't try to learn from the losses and the mistake they ever made.