The critical point here is he's saying it because he's read it in a book, and it rang true.

That means he had good upbringing or just good life intuition to recognize that to be a good idea.

Wisdom is knowing in your bones, that something's true. Thompson's merely trying to convey what others have conveyed to him, coupled with some intuition.

Which's my entire point - don't bother listening to people regurgitating something they read in a book, go find folks who've lived it. They tend to be older :)

So if a 50-year-old wiseman writes a book, a 20-year-old reads it and copies its ideas into a letter for a friend in need of some wisdown, and I read the letter 60 years later, what do I do? To help with the prescription: I'm in my mid-twenties and, as you now understand, quite a simpleton.

I'd like to throw in that Meditations by Marcus Aurelius is quite a famous staple of stoic reading, but it's mainly a compilation of lessons from other great stoic teachers that resonated with him.