[30a middle] Abaye: It is better for Jews [who will not change their ways] to err unintentionally, rather than to make their inappropriate ways known to them and they now sin knowingly and intentionally. [This was stated in regards to sitting at the end of an alleyway next to the end of an Eruv (where one might inadvertently drop an item outside of the allowed carrying limit and want to bring it back in) and the practice of people clapping and dancing on YomTov]. This teaches us to apply rebuke only to someone who will listen. The Germarah however adds, that regarding an explicit Biblical law [or when a violator may actually mend his ways], we still should rebuke others.
T’s lesson: We should not be quick to rebuke others. We must properly assess and analyze each unique situation accordingly. Try to recognize what gain (if any) will come from our actions, and always THINK before we DO.