This document introduces concepts from behavioural economics, which challenges the assumption that people always make rational decisions. It discusses how social, emotional, and cognitive factors can influence choices. People have bounded rationality and use mental shortcuts like heuristics. Choices are affected by defaults, framing, norms, and biases. Behavioural economics aims to "nudge" better choices through approaches like changing defaults or using social norms, rather than mandates. However, some argue that nudges could be seen as paternalistic or that consumers are not as irrational as behavioral economics assumes.