"People who live in glass houses should not throw stones" reminds us that we should be careful how we treat other people (with our words and actions) because we can all be easily hurt. People "throw stones" at other people to try to hurt them, and one way that people try to hurt other people is by saying bad things about them. If you lived in a "glass house" it would be very easy for other people to hurt you by throwing stones at you. "People who live in glass houses should not throw stones" means that we should not say insulting things to other people because they could easily do the same thing to us. Example: "Look at that shirt you are wearing! Did you buy that back in the '80s?!" Answer: "Hey, you're not so young yourself; people who live in glass houses should not throw stones!" Something made of glass can easily break; it is vulnerable; and we are all vulnerable in different ways. Sometimes we forget our own vulnerability and "throw stones" at other people in the form of criticism. A person might remind us that we too have our own faults and weakenesses by saying "people who live in glass houses should not throw stones". Example: "Look at what time it is... you are late again!" Answer: "Hey, how often are you not on time? People who live in glass houses should not throw stones."