People who are materialistic are more likely to be depressed and unsatisfied, in part because they find it harder to be grateful for what they have, according to a study. "Gratitude is a positive mood. It's about other people," said the study's lead author. "Previous research finds that people are motivated to help people that help them." But materialism tends to be "me-centered." A material outlook focuses on what one does not have, impairing the ability to be grateful for what one already has, researchers said.