In short, Stoicism is a tool set that helps us direct our thoughts and actions in an unpredictable world. We don’t control and cannot rely on external events, but we can (to a certain extent) control our mind and choose our behavior.
In the end, it’s not what happens to us but our reactions to it that matter. - What Is Stoicism? A Simple Definition & 10 Stoic Core Principles
I think the following quotes speak for themselves:
Waste no more time arguing what a good man should be. Be One. – Marcus Aurelius
What really frightens and dismays us is not external events themselves, but the way in which we think about them. It is not things that disturb us, but our interpretation of their significance. - Epictetus
Until we have begun to go without them, we fail to realize how unnecessary many things are. We’ve been using them not because we needed them but because we had them. - Seneca
The good or ill of a man lies within his own will. - Epictetus
It is not the man who has too little that is poor, but the one who hankers after more. - Seneca
External things are not the problem. It’s your assessment of them. Which you can erase right now. – Marcus Aurelius
Let us prepare our minds as if we’d come to the very end of life. Let us postpone nothing. Let us balance life’s books each day. … The one who puts the finishing touches on their life each day is never short of time. - Seneca
Keep death and exile before your eyes each day, along with everything that seems terrible— by doing so, you’ll never have a base thought nor will you have excessive desire. - Epictetus
No person has the power to have everything they want, but it is in their power not to want what they don’t have, and to cheerfully put to good use what they do have. – Seneca
Never let the future disturb you. You will meet it, if you have to, with the same weapons of reason which today arm you against the present. – Marcus Aurelius
It reminds me not to look always for getting more, avoid buying stuff I don’t use in the end, that in every bad event there is something good you can get out of it, that in the end it’s me who decides no one else is responsible for my decisions, try to avoid thinking about the past and the future instead focus on the present, no one else is responsible how I feel.