An economist develops a theoretical framework to explain short-term changes in a country's total economic output. The framework only considers two factors: the level of government spending and a measure of overall consumer optimism. The framework accurately predicts a six-month period of declining output but fails to predict the strong economic rebound that follows. Based on the purpose of such frameworks, evaluate the likely reason for this model's failure and justify whether it should be considered a useful tool despite its inaccuracy in this instance.