Don’t bite off more than you can chew: that is basically the message that Epictetus is conveying in the thirty-seventh chapter of the Enchiridion. While we all strive for the best in ourselves, we should moderate our spirit to what we can actually achieve at any given time. Slow and steady wins the race.
If you have taken on a role that is beyond your power, you have not only acted poorly in that role, but you have also passed over what you could have fulfilled.
Stoics are sometimes perceived as idealists. And that’s usually a good thing. The virtue of courage stimulates us to give our best in all situations. On the other hand, we should be realistic and acknowledge what is possible and what is impossible. This is informed by the virtue of moderation.
Stoicism is above all a rational philosophy. Some actions are simply beyond our strength. If you attempt to become an ideal Stoic Sage immediately, then you will be disappointed. In fact, you are very unlikely to reach that ideal at all by unrealistic attempts. A steady pace towards the ideal is better than erratically jumping around. If you attempt to make progress towards that ideal, in a pace that you can keep up, then you are doing the best you can. Then you are really making progress.