What does it mean to be a Stoic? I think there are several things that it takes to define a Stoic.
First, you must know what it’s like to suffer. Everyone has this quality. You’ve probably been called a name or you’ve been rejected by a loved one. Perhaps you’ve felt powerless because of some injustice. Maybe you remember how you overreacted to a situation and made the situation worse than it would’ve been. You said something that you can’t seem to forgive yourself for.
Second, you’re looking for a solution to life’s problems which could mean a solution to all your problems. And most importantly you’re not looking for something that is a band-aid or sugarcoats your problems. You’re tired of making yourself mad or regretful over things that were years ago and shouldn’t matter. You’re looking for something rational and not a rationalization. You want a philosophy of life.
Third, you believe that thinking and wisdom can solve your emotional problems. This doesn’t mean you think you can just cover up your feelings, suppress them, and begin thinking in purely logical terms. It’s not that easy. If it were that easy, then the Internet wouldn’t be full of people who insult each other while pretending their feelings aren’t hurt. You have to realize that a lot of our negative emotions, which the Stoics called pathe (suffering), are a result of our voluntary judgments about the world. When we realize that our suffering is caused by incorrectly evaluating external things like wealth, health, reputation as good, and incorrectly evaluating things like poverty, sickness, and ill repute as bad, much of our suffering will stop. When we realize that anything outside what is up to us such as our judgment and will, things will go simply.
Fourth, you believe that the only thing truly good is virtue or a noble character. Your character is up to you because it is part of your judgment and will. When you realize that only a noble character is truly good and the lack of virtue is the only bad, then you’ll suffer significantly less. Since poverty and sickness aren’t to be evaluated as bad, then they shouldn’t disturb you like they did before. Also vicious people shouldn’t disturb you nearly as much because you’ll learn that a vicious person lacks practical wisdom and self-control. A vicious person is only vicious because they’re not actually wise to the fact that virtues like practical wisdom, justice, moderation, and courage are the true goods. A vicious person is foolish and is the cause of their own suffering. Sometimes their suffering can spill over and cause problems for others. But ultimately it’s hard to be angry at a person who is pitiful, incompetent, and a slave to their impulses.
Fifth, you believe that living a life of virtue means being in harmony with those around you and with the cosmos. Being virtuous means living in agreement with nature. You have learned that reason isn’t a mere means to some good but is the good that must be served in the form of universal love. Every human being is united as citizens of the world or the universe. Individuals, families, creeds, tribes, and nations are all secondary to the sea that is humanity and all rational beings throughout the universe. This is what the Stoics meant by cosmopolitanism which they inherited from the Cynics.
There’s a lot to being a Stoic. But if you possess those five defining qualities above, then you’re more or less following Zeno of Citium’s philosophy of Stoicism.