Stoicism is Weird
Stoicism should feel counter-intuitive.
If you've ever read a modern text on Stoicism, such as The Obstacle is the Way by Ryan Holiday, and found yourself nodding along to common-sense maxims and inspiring stories, you've been robbed.
Stoicism is a powerful philosophy that can transform you. It can transform you because it's weird. That is, it's not already how you think. It's a very different way of thinking that should make you skeptical at first.
The Stoics taught that you should be as unbothered by the breaking of your favorite cup as by the death of your loved ones. They taught that anger was always a mistake. Along with other negative emotions. They say you should be indifferent to things you currently are probably not, like wealth and fame. They teach that you should think about worst-case scenarios -- which is something most people avoid -- and suggest that you can be happy in the worst of circumstances.
I'm not going to explain Stoicism in detail here. My point is that the Stoics present a strange and counter-intuitive philosophy that shouldn't make sense to you at first. It makes perfect sense to me now that I have internalized it. I am almost never angry. It happens infrequently enough that I can remember the last time I was somewhat angry, and it wasn't this week or the last. In order to be angry, you have to believe the world owes you something, and the Stoics will cleanse you of that misapprehension. If you read the original Stoics, that is.
But modern proponents of Stoicism try to make it more appealing for a modern audience. In doing so, they rob the philosophy of its power. Stoicism should not be appealing! Stoicism is an alien way of thinking. If you don't feel like what you're reading is bizarre compared to the normal human way of thinking, then you're not reading Stoicism!
Personally, I recommend the Enchiridion by Epictetus. Of all the Stoics, he is the most direct.