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.
trade is the emotional game of actors and ambition, if we want to get profit then we can control our emotions and ambitions, because both will always destroy us in trade, calmness in trade can save us from heavy losses if prices fall we are not trapped in a panic .
I should not call it an emotional game as that would never help you to be profitable.
We are trading for profit and we don't use our emotion to be profitable, therefore we should stick to the strategy that could make us profitable, it should be our mind and not our emotion. Not being able to control your emotion will likely result to bad decision.