While it is very difficult to mess up a dish of fried rice, America’s Test Kitchen points out that making the dish perfectly comes down to the texture of the rice that is used, and leftover rice — because it’s been allowed to undergo retrogradation wherein the rice grains dry out and firm up — offers a better texture to work with versus fresh rice, which is too soft not to turn mushy during the frying process.
While medium-grain rice works best for cooking fried rice as described, most recipes — regardless of the oil, flavoring, and add-ins — call for the use of leftover rice. As Culinary Lore explains, freshly cooked rice is fluffy and hot and perfect for eating as is, but contains too much moisture. The texture of leftover rice (dried out), on the other hand, is the perfect texture for a dish like fried rice because of the reintroduction of moisture. Fresh rice will turn out mushy or soggy due to having too much moisture in each individual grain of rice.
This said, you can still make killer fried rice with freshly cooked rice. Just remember to take the rice, spread it out on a baking sheet and let it cool a bit before using. (America’s Test Kitchen recommends 10 minutes to achieve room temperature, then another 20 minutes in the fridge.) Doing this allows the freshly cooked rice to mimic the quality of leftover or day-old rice; the rice grains dry out and are ready to become part of a flavor symphony that is far greater than the sum of its parts.