This quote is so true because people don't actually think abut what they say or if they could've hurt someone. It can be very easy to hurt someones feelings, for example if you say "you're so stupid" that can hurt someone even if you were just joking. Some people don't get hurt as easily but everyone's different and reacts to things differently so it's better to be kind and avoid saying anything mean because you don't know how badly if can effect someone.