Nothing good is a joy to have without a friend to share it.

Where this comes from

Seneca wrote letters to his friend Lucilius nearly 2,000 years ago. In this one he says he loves learning things so that he can pass them on, and that even wisdom would give him no joy if he had to keep it to himself.

How you could say it to a five-year-old

“You found a shiny shell? Who do you want to show it first?”

Seneca, Letters 6.4. We put these lines into plain English ourselves, staying close to the original and to public-domain translations.