Gratitude means more than simply saying thank you. Researchers usually define it as a feeling or state that results from both (1) recognizing a good thing, such as a positive outcome or gift we’ve received, and (2) recognizing that this good thing came from outside ourselves. Although we most often experience gratitude in response to the actions of other people, we can feel grateful to nonhuman sources, too, such as nature, a higher power, or the universe.

Several studies have investigated the nuances of gratitude, finding that three factors tend to increase the amount of gratitude people feel for benefits they’ve received: the more purposefully someone has helped us (as opposed to unintentionally or with an ulterior motive), the more they’ve sacrificed to do it, and the more the outcome benefits us, the more grateful we feel.

A high school student writes a gratitude letter to his grandmother for taking over his evening responsibilities while his parents worked so that he could study for his finals. She missed her weekly gatherings with friends and instead watched his younger siblings and made them dinner every night, leaving the high schooler ample time to study. As a result, he passed his finals with flying colors!

Though even toddlers can be taught to say thank you, children seem to first experience and express true gratitude at around 6-8 years old, when they are more capable of taking another person’s perspective and have a greater understanding of another’s emotions. Gratitude curriculum has been shown to work with students as young as eight, increasing not only their levels of gratitude but also their social and emotional well-being.