I am using a the exposition here, not the actual quote from Marcus Aurelius. I find it much easier to meditate on. The original is confusing.
Consider your place in the universe next time you feel self-important, or like everything rises and falls on what you do next. It doesn't. You're just one person among many, doing you best among many. That is all you need to do.
paraphrased from Marcus Aurelius
This could be read as "you are unimportant". But it also reads that simply because we are not the most important thing in the universe, it does not mean you ignore your worth. Persevering regardless is all we can or should do. But that doesn't diminish our efforts. We are good, or moral, or helpful based on our actions, not our importance.