Happiness in this world, when it comes, comes incidentally. Make it the objet of pursuit, and it leads us a wild-goose chase, and is never attained. Follow some other object, and very possibly we may find that we have cought happiness without dreaming of it.
孔子说:“温习旧知识时,能有新收获,就可以做老师了。”
The most difficult thing is to be simple.