Someone says something about you and you get rattled for the day. Your son or daughter lashes out at you—and your week is thrown off. You overhear someone saying something about your appearance—and it gets to you. Your boss lays into you—and now you’re anxious and insecure. All of us—every single one of us—have experienced this. No one is immune to the judgments of others.

And yet: Why do we put so much stock in what others say? Marcus has a clever observation: “We all love ourselves more than other people, but care more about their opinion than our own.” It’s true isn’t it? We’re generally selfish people but the one thing we value more than ourselves is other people’s opinion about us. And this ridiculous contradiction causes us so much misery.

One of stoicism’s fundamental principles is that we all have a “citadel of the self”: a fortress that we’re constantly building and strengthening. That fortress can only be breached by us, when we let an opinion or a thought go past the walls. Whether that happens—whether we give ourselves over to someone else’s judgment, opinion, slur, thought, action—is a choice.

Nothing outside of your own thoughts can affect you—if you choose. No one’s opinion of you can shake you—if you don’t allow yourself to be affected by it.