You don’t have ten thousand years. Be good while you can.

Where this comes from

Marcus Aurelius reminded himself in his private notebook not to act as if he had ten thousand years to live. Life is short, he wrote about 1,850 years ago, so be good now, while it is still up to you.

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

“Your friend is sad now. You can ask, ‘Can I sit with you?’”

Marcus Aurelius, Meditations 4.17. We put these lines into plain English ourselves, staying close to the original and to public-domain translations.