The phrase "how the other half lives" refers to the living conditions and lifestyle of a social class or group that is different from one's own. It is often used to describe the stark contrast between the wealthy and the poor, or between those who have privilege and those who do not. The term was popularized by the American journalist Jacob Riis in his 1890 book of the same name, which exposed the harsh living conditions of the working class in New York City.
In general, the quote "how the other half lives" is used to highlight the inequalities that exist in a society and to promote greater understanding and empathy between different social groups. It can also be used as a call for social reform or change.