Utility Theory helps us understand how people buy things, especially when the economy changes. But, it doesn't always predict what people will do perfectly. Here are some important points to remember:

1. Utility Function: People try to get the most satisfaction (or utility) from what they buy. This satisfaction depends on what they like and how much money they have. We can think of it like this: the happiness from buying items depends on a mix of all the things they choose to buy.

2. Income Effect: If someone gets a 1% raise in their income, they might spend about 0.5% more on things they usually buy.

3. Substitution Effect: If the price of something goes up by 10%, people might buy about 7% more of similar items instead.

4. Limitations: There are times when things don't go as planned. Factors like how people feel, changes in the market, and unexpected events can mess up these predictions.

In short, Utility Theory gives us a peek into what people might do when things change in the economy, but it doesn’t always tell the whole story!