Both happiness and unhappiness depend on perception

Nothing that goes on in anyone else's mind can harm you.

Everything is born from change. ...there is nothing nature loves more that to alter what exists and make new things like it. All that exists is the seed of what will emerge from it. You think the only seeds are the one that make plants and children? Go deeper.

Mark how fleeting and paltry is the estate of man - yesterday in embryo, tomorrow a mummy or ashes. So for the hairsbreadth of time assigned to thee, live rationally, and part with life cheerfully, as drops the ripe olive, extolling the season that bore it and the tree that matured it.

Anything that is beautiful is beautiful just as it is. Praise forms no part of its beauty, since praise makes things neither better nor worse. This applies even more to what it commonly called beautiful: natural objects, for example, or works of art. True beauty has no need of anything beyond itself.

Confine yourself to the present.

The wise man sees in the misfortune of others what he should avoid.