Everyone seems to have a clear idea of how other people should lead their lives, but none about his or her own.

This quote means that many people have strong opinions about the ways others should live their lives, but are less sure about their own. For example, someone might say that their friend should quit smoking, but be unsure about the best way to manage their own finances. This quote suggests that, perhaps put more thought into understanding our own actions and motivations, rather than being so quick to judge the actions of others.