I wish to explain what this statement actually means and how important it is to everyone.
The first time I came in contact with it, it was like a turn off to me, but later I understood it and why it stands that way. But to some it presents a negative attraction to them. Human beings like to do what they are told not to do because they thought it was good that's why you are trying to prevent them from doing it, but this is not the same with this.
Now this idea helps isolate your mind from unnecessary worries after you have invested your money, and enables you to make intelligent decisions especially during the bear market. Particularly the day traders find it very useful daily, and of course for long term holds. The thought will give you the mind to hold your coins till profit and prevent you from selling at loss.
It does not mean in any way that you will lose the amount you are investing, but also if it happens you will not need to commit suicide because it happened. This is a preventive measure to save your heart from unexpected occurrences should it happen.
In actual sense, "Don't invest more than you can afford to lose" only helps you not to lose your money finally.
Remember that intelligent trading decisions cannot be made effectively with your emotions active, so avoid trading with high emotions.
Happy trading guys
What else would that mean is just we don't want to do anything if we don't have enough money to invest in. People tend to chase money even though they don't have the actual ammunition for it.