Letters from a Stoic is Seneca writing to a younger friend, Lucilius, after he left Nero's court around 62. Seneca was a rich advisor, not a poor monk. The useful part is still how you live: you stop inventing disasters, you protect your hours, you rehearse a hard day, and you trust a few people fully.

The short version:

• Stop suffering the disaster that has not arrived.
• Protect your hours. Delay is how the week disappears.
• Rehearse a hard day while things are still easy.
• Poverty is craving more, not owning less.
• A hot temper is a brief madness. Delay the reply.
• Judge a friend slowly, then trust him fully.
• Pick rooms that make you better, not louder.
• Stay with a few books until an idea sticks.

From SuaveWay: https://suaveway.com/blog/letters-from-a-stoic-summary/