Punishment is always necessary when a child breaks clearly stated rules, but you need to be sure to discuss why they're being punished. It's also good to make them aware of a stricter punishment if that rule is broken again. However, if you've never had a conversation about a certain thing, they do not deserve consequences, but to be educated on why their decision was wrong. The second time around, though, grounding/loss of privileges is more than deserved. They'll definitely despise you for a while, but what kid doesn't? Mistakes help people learn, and I don't think it becomes an actual problem until they become a repeat-offender.