Final answer:
When economists assume that people are rational and respond to incentives, they mean that people act in their own self-interest.
Step-by-step explanation:
The assumption that people are rational and respond to incentives, as economists do, means that people act in their own self-interest. This means that individuals make decisions based on what they believe will bring them the most benefit or utility. It does not necessarily mean that people always act selfishly or without regard for others, as individuals can also have altruistic tendencies and care about the well-being of others.