Microeconomics production and consumption/Rational consumer

"We have budgets and must decide how to spend them. The model of utility theory that economists have constructed to explain consumer choice assumes that consumers will try to maximize their utility....

"Utility theory provides insights into demand. It lets us look behind demand curves to see how utility-maximizing consumers can be expected to respond to price changes. While the focus of this chapter is on consumers making decisions about what goods and services to buy, the same model can be used to understand how individuals make other types of decisions, such as how much to work and how much of their incomes to spend now or to sock away for the future." - Principles of Microeconomics