“You shouldn’t give circumstances the power to rouse anger, for they don’t care at all”

Marcus Aurelius’ quote illustrates the fact that getting upset at your circumstances does little to help your situation. Getting upset at another person usually doesn’t do much good for you, but at least a person can be interacted with. Being angry with something that isn’t alive does no good at all.
Of course, that doesn’t mean that it isn’t normal to be angry at a circumstance or set of circumstances that makes your life difficult. It is perfectly reasonable to be upset about something that happened that derailed your life.
But when your anger at something that happened to you turns into wanting something to validate, or even acknowledge your feelings of frustration, it can lead you into an even deeper spiral, when you find that nothing cares, or even acknowledges your feelings.
It should be noted that being angry that something bad happened to you is not the same as being angry at a non living thing and screaming int the void. I think that Marcus Aurelius’ quote is more aimed at people who start at the former, but eventually move into the latter.
But if done in a measured way, being angry at something can be a way to let out your anger. You don’t want to have feelings pent up inside you just because you don’t want to show any emotion.
When people say they hate cancer, or want to beat cancer, they are anthropomorphizing cancer as a way to focus their resistance to the disease. If those same people every day screamed into the mirror, “cancer, I hate you,” that would be a problem.
But maybe the biggest lesson from this quote is that it is critical to be able to move on from anything that happens to you. Outside of a few good family and friends, the world is largely indifferent to what happens to you, positive or negative. We all deserve to have time to be upset and vent in our own way, but we have to also learn how to get past what happens to us and keep moving forward.