Daniel Gilbert opens Stumbling on Happiness with his foundational, research-grounded premise: humans are systematically, predictably poor at accurately forecasting what will genuinely make them happy in the future, consistently overestimating both the intensity and duration of their emotional reactions to anticipated future events.

Gilbert's foundational argument:

• Drawing on his own extensive psychological research career, Gilbert presents evidence that people consistently mispredict their future emotional responses — both positive and negative — to anticipated life events, from career changes to relationship outcomes to significant purchases
• He argues this prediction failure isn't random or occasional but reflects systematic, identifiable cognitive patterns and biases that consistently distort this specific type of future-oriented emotional forecasting, distinct from more general reasoning or memory
• Gilbert's engaging, often humorous writing style throughout the book makes this research-grounded argument accessible to general readers, distinguishing the book from more purely academic psychological writing on similar topics

This foundational premise sets up the book's overall project: examining the specific cognitive mechanisms underlying this consistent mis-prediction of future happiness, addressed through subsequent chapters on memory, imagination, and the specific biases distorting this predictive process.