Likewise in gambling, the summary of it is to trade only what you afford to lose.
My addition to it is to strengthen your emotion.
The difference is that in trading you need to study hard before making a decision. Emotion plays a crucial role as well but it is not the main reason. I think that people act more in panic in gambling rather than in trading.
Traders do not need to panic sell because the market can be manipulated easily so before taking any decision, we should do our own research.