The act itself does not constitute guilt unless done with a guilty mind.
It is a Latin maxim, which means that for any act to be illegal in nature it must be done with a guilty mind. Hence, act done without any intention cannot be punished. Not only is the act of the accused important but also the intention of the accused to do the specific act is equally important to prove the guilt of the accused. Hence, it can be said that mere breach of law is not sufficient to constitute a crime.
‘B’ attacks ‘A’ with an intention to cause grievous hurt or injury then it is a crime because it included a guilty mind. But when ‘A’ was attacked, it caused injury to ‘B’ in private defence then it is an unintentional act and hence, it cannot be considered as a crime.