We read many times that a particular deva/person/asura was given a boon that he could e.g., become invincible, no one can kill him or will get something or the other.
On the other hand, some people are cursed that something bad will happen to them either immediately or after some time.
I wanted to know how can a person say something (good or bad) about another person and Gods/nature will fulfill that. In case of Gods, it is still ok to an extent that they can do anything, but for mortal persons to be able to give a boon or curse is something which is confusing.
Even in case of Gods, e.g., if they give a boon to someone that he cannot be defeated in a war, how will they make sure that he will only fight with ones who are less powerful than him and not stronger?
So what do Gods/people do for their boon or curse to really work?