>>this is a kind of proverbial statement , which highlights different aspects of life too other than trading.
But in trading and as a trader it's helps you be a bit rational and less irrational in decision making, rather than being emotional when you have losses in trading, you should actually see it as something that's always meant to happen. Its like a learning process that never ends.
Anytime you trade always be self prepared for losses, but at the same time keep your hopes high for positive results.
Yea it's actually the best mindset to start with, by calculating your loss before your profit, it's all what most of this experience and profitable traders do, they mostly calculate how much they are willing to lose on a single trade, before calculating how much they are going to eventually make, and the best way to go about it is by trading with an amount you can afford to lose, so in my own perspective, as a trader, that's the beginning point of knowing exactly what you are doing.
And this is what separate the profitable traders from every other traders, they knows that in trading, knowledge on technical and fundamental analysis alone is not enough, you need patience, and the ability to control your emotions, you need to be very good in managing your risk properly, so in essence of what am trying to say is that, just as the op of this thread has rightfully said, it's very important as a trader to calculate his or her loss first before calculating his potential profit, so that his or her emotions can be in check.