Every season brings an abundance of fruits and vegetables. In most of the United States, June means tasty blueberries and strawberries. September and October feature crisp apples and acorn squash. In most cases, buying what's in season in your growing zone means you have the best tasting and freshest produce. Much of the produce sold in stores has a long shelf life because it has been grown from seeds selectively bred for that very characteristic. Unfortunately, this practice sacrifices taste. Buying fruits and vegetables in season most likely means you are purchasing them locally, negating the need for produce that can withstand being trucked across the country.
But don't beat yourself up if you live in Maine and want an avocado in January. It's a fact of life that some of the produce you love doesn't follow your region's growing cycle. Buying most of what you eat in season helps to offset the impact of transporting food long distances, so enjoy.