Epictetus

Men are disturbed not by things, but by their opinions about them.

Every habit and faculty is preserved and increased by the corresponding actions.

Nothing great is produced suddenly, since not even the grape or the fig is.

Some things are within our control and some things are not. Within our control are opinion, motivation, desire, aversion, and our actions. Not within our control are our body, property, reputation, and office.

If you wish to improve, be content to appear foolish and stupid regarding externals.

He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

It is not things themselves that trouble us, but our judgements about those things.