Context
My informant had first heard this proverb in middle school, when a kid was sad and the teacher made a silly face. The environment got more lighthearted and the teacher used it as an example of how the proverb, “laughter is the best medicine,” works in action. They have noticed that it still works to this day, as they have found that usually when you try to make people laugh in an appropriate situation, the mood gets better. They notice laughter works too when they are feeling down.
Typically they use this proverb in friend settings when things seem sad. While the lesson in the proverb holds true, saying the proverb can also work, if said in a joking manner.
My informant still believes in the proverb because they have seen it happen in real time and because it has happened to them. Their personal experience enforced their belief in the proverb.
Analysis
In comparison to some other proverbs said to children, like “don’t put all of your eggs in one basket” and “actions speak louder than words”, “laughter is the best medicine” is surprisingly positive. This may be due to a more peaceful upbringing than in times of war. My informant told me that this proverb may have originated from the bible verse Proverbs 17:22 “A merry heart does good, like medicine.” The more modern version may have been simplified to be understood easier by children.