Material things, along with the ways they are marketed, move our focus onto ourselves rather than others. In this way, materialism can cause us to quietly reject the Lord's commandment to "love thy neighbour as thyself" (Matthew 22:39).
This focus on self and the stuff of this world is not part of living "after the manner of happiness" (2 Nephi 5:27). In fact, modern research seems to have verified that (1) you can't buy happiness and (2) a focus on others can bring greater personal satisfaction.5
As Elder Joseph B. Wirthlin of the Quorum of the Twelve Apostles (1917–2008) taught, "We are happiest when our lives are connected to others through unselfish love and service."6