I find this suggestion by Marcus Aurelius uplifting because it encourages appreciation, awe, optimism, positivity, and a sense-of-wonder. But I offer this variation and interpretation as food for thought...

Dwell on the beauty in life and your spirit will soar to the heights of joy.

In contrast, if you primarily focus on the lack of beauty, of the lack of anything (limitations, what's wrong, the negative, etc) you will experience the opposite of joy — fear, stress, anxiety. And by The Law of Attraction you will draw more of the negative stuff you focus on into your life. You are aware the you are a creator and that your are creating your reality with your very own thoughts and what you focus your attention on, aren't you?

Stay positive, see only the good, and expect wonderful!