Riddle: You must keep this thing, its loss will affect your brothers. For once yours is lost, it will soon be lost by others. What is it?
When you first heard of the riddle, you may have thought that what is lost is some kind of object, but it is your temper. If you lose your temper, you suddenly become so angry that you shout at someone or show in some other way that you are no longer in control of yourself.
Therefore, its loss affects the people around you, like your brothers. In addition, when you lose your temper and shout at your brothers, they will easily get irritated and lose their temper.
The answer of this riddle is your temper.