I propose that in their social interactions, people may be energized by egosystem motivation in which they are preoccupied with proving their own worth and value to themselves and others, or by ecosystem motivation in which they strive to be constructive and supportive of people and things they care about beyond themselves. These two motivational systems, I suggest, are scaffolded onto evolved motivational systems for self-preservation and species-preservation, and have profound and sometimes paradoxical consequences for people’s own psychological experiences, health, and well-being, their relationships, and the people around them. I will describe my current thinking about these two motivational systems, and then present research on how egosystem and ecosystem motivation predict relationship processes and outcomes and psychological well-being for oneself and others across relationship types (strangers, roommates, friends, romantic relationships), in good times and bad.