The first book of Epictetus’ Discourses revolves around ten themes which are also repeated in other places throughout Discourses. The first book lays down the foundations of Stoicism, as expounded by Epictetus. The Stoic Gym has so far released thirty blogs covering the entire Book 1 of Discourses, presented in plain English (thestoicgym.com). In this blog, we explore the basic themes of Stoicism covered in Discourses Book 1.
Concern yourself with only what is in your power.
Unlike other animals, we have the ability to reason. Reason enables us not to get carried away with first impressions but judge them properly. This is the only thing we need to do to live well. Instead, we concern ourselves with so many external things – such as wealth, reputation, and the way we look – that are irrelevant to our living well. We have control over certain things in life but not over others.
We make ourselves miserable by trying to control things that are not under our control and failing to control things that are. Train yourself to be concerned only with what is under your control and not with things that are beyond your control. 
Be content to let things happen as they do.
The law of life is to live in accordance with nature. You are responsible only for things under your control. We always have the option of choosing what happens, as it happens. [26, 12, 25]
Your thinking, not the externals, drives your behavior.
We act according to the way we think. Our thinking drives our behavior. By changing our thinking we can act differently. Never blame outside forces for your behavior. 
Do not place value on external things.
It is not antisocial to be self-interested. But placing value on externals make us become subservient to others and creates conflicts. We create our own problems by choosing to attach value to external things. We are social beings. External things are of no value. Our fear and envy are the result of valuing external things. External impressions can be deceptive. Good and evil come from our choices, not from externals. [19,25, 23, 24, 27, 29]
Evaluate your first impressions using reason.
We get into conflict because different people interpret the same impression differently. Placing value on externals results in contradiction and conflict. [20, 21]
Don’t give in to your anger or animal instincts.
People act in a way that appears right to them. So anti-social people such as thieves are misguided and deserve our pity, not hatred. We get angry at such people because we value external things (such as our property). [3, 18, 28]
You can handle anything; always act your best.
No difficulty in life in unbearable as long as you can find a reason for it. So always act your best, even if you can never be as good as the best. Be diligent in your pursuits.
Don’t be upset if things don’t happen the way you expect them to, Don’t put yourself above others even when you have authority over them.
Don’t seek admiration. Be well-grounded.
Don’t envy others. Be aware of god’s gifts and be constantly thankful.
You have all the resources you need. Choose the right tool for the right job. For example, to combat a habit, choose a counter habit.
You have no reason to complain. You have all the resources you need to copy with any challenge in life. Understand this and don’t complain. God watches over us. Have these principles handy at all times. [2,10, 13, 21, 16, 24, 27, 6, 14, 30]
Learn to think properly and logically.
Beware of rigid thinking. Learn logic so you can think logically. Learn what is important in a given context and don’t be carried away with things that are incidental. We need logic to understand what is true and what is false. [5, 7, 8, 17]
Practice, not knowledge, results in progress.
Nothing happens instantly. Be patient. Difficult times reveal what we are made of. Difficulties are opportunities for training. Play wholeheartedly or leave. Be steadfast in your practice. [4, 15, 24, 29]
Only you can make you unhappy.
Only you – not others – can make you unhappy. Remember your divine aspect and you have no need to worry. Be a citizen of the universe. 
Numbers in square brackets refer to the Discourse in Book 1 where the theme is expanded.