It is hard
If, abusing the child, the adult smiles or still somehow expresses the sympathy or if one of parents reacts to his behavior differently, than another, at best the child will appear in confusion, and in the worst education will not take effect in general or will cause the return reaction.
It is hard for adult to understand that they encourage pranks, uncontrollability, precipitate or unacceptable acts in society.
Not easy to notice that you approve acts which were absolutely natural at earlier stage of development, but now became inadmissible the child grows and it is necessary to stop gradually encouragement of earlier permitted actions, and then and to start condemning them.
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