Full Idea
There are three essential conditions for peace of mind: autarchy, apathy and freedom. Autarchy is self-government and self-sufficiency; apathy is indifference to what the world can do to you; the freedom is from dependence and possessions.
Gist of Idea
For peace of mind, you need self-government, indifference and independence
Source
Diogenes (Sin) (reports [c.360 BCE]), quoted by A.C. Grayling - What is Good? Ch.3
Book Reference
Grayling,A.C.: 'What is Good? The Best Way to Live' [Phoenix 2003], p.42
A Reaction
Quite good advice, but I don't see 'peace of mind' as the highest human ideal. The basic suggestion here is live alone and do nothing. Certainly don't get married, or have children, or try to achieve anything.