It applies to adults as well. The important premise to remember is that people are better able to see the mistakes in other people’s behavior than in their own.
Preschool age children recognize others making mistakes and breaking rules before they can recognize themselves making mistakes and breaking rules. Kids tattle on each other. Young children often tattle on others while they are violating the same rules they are tattling on!
Followers of Vygotsky view tattling as an important step in being able to regulate one’s own behavior and would never advise punishing a child for tattling!
In other words, recognizing other kids bad behavior is an important step before a child can learn self-control. So when a kid tattles, don't automatically punish the tattling. Turn tattling into a learning experience. If you witness the same behavior, say, "You're right. I'm glad you noticed that." or "That's not the best way to handle it." If you did not witness the behavior, ask, "What do you think of that behavior?" "What might be a better way for them to handle it?" "What would you do?"