Well, this was one of the first thing I was thought even before laying my hand on any book. It comes with the popular Forex term of "do not invest that which you cannot lose". In the actual sense, I have set out the extent at which I see as my own loss bearing point in every 24 hours and each time I hit that point, I close the trade for the day.
Yes that is a common sense risk management which all people should know without being told, often some lose are incurred due to people actually invest what they can not afford lossong so the panic and presssure gets higher while trading. Which eventually leads to trading with confusions and emotions instead of logical.