Here's why:

* Structure: Esters are formed by the reaction of an alcohol and a carboxylic acid. The characteristic fruity smell comes from the combination of the alcohol and acid moieties.

* Volatility: Esters are generally volatile compounds, meaning they evaporate easily. This allows their aroma to reach our noses.

* Wide Range of Scents: Different esters produce a wide variety of fruity smells, ranging from sweet and floral (like banana or pineapple) to more tart and citrusy (like orange or lime).

Therefore, if you encounter a compound with a distinctive fruity smell, it's likely an ester.

However, it's important to note that not all esters have fruity smells. Some can have other odors, like those found in artificial flavors or fragrances.