"If you choose to hold fast to what is right, do not be irked by difficult circumstances, but reflect on how many things have already happened to you in life in ways that you did not wish, and yet they have turned out for the best." Musonius
Since there are even people who strive and suffer working on endeavors that are illegal and immoral, how much more so would you be willing to strive and suffer working on endeavors that are noble and awe-inspiring? These worthy ventures are not necessarily for others to admire but they are taken to test your endurance and stamina such that you would impress even yourself. For until you have earned the respect of yourself, you cannot assume you can gain the respect of others.
When you have earned your own respect, it is real. Even if you are able to fool everyone, you cannot fool yourself. You know exactly what you are thinking at anytime, how hard you have actually pushed yourself, how you weathered unfairness yet did not lose focus, and whether you were able to resist temptations that overcame you in the past. Even if you did try to fool yourself, you will fail because in the back of your mind, you know it is not real.
However, once you have worked hard, persisted, and finally earned your confidence, you are impervious to the opinions of the world. If someone speaks ill of you, you would discount it immediately because it is so blatantly false. It would be like if someone accuses you of lying and you know you did not, no amount of evidence could possibly satisfy that person, yet you know the entire truth. If it was possible for him to read your mind, you would let him, but he cannot. Indeed you would be more concerned about that person's obvious ignorance than being concerned about yourself, and would try to convince him if possible.
Even if the entire world were to say you are only worth such and such, would you doubt yourself and believe it? No, you would not. You have already tested, realized, and confirmed your value. Your worth is not determined by others and what they think -- since they can be fooled -- but determined by a substantially more reliable source who knows you more than anyone: yourself.
How do you test yourself? By making decisions that are different than the decisions you made in the past under similar circumstances. For example, if you normally gorge on food in the afternoons, make it your goal that you will not do so this afternoon. You will have success if you are patient and not try to do too much all at one time. Like a baby who has never walked before, you cannot run right away, but must concentrate intensely for even taking one small step. It will be difficult at first, but everything worthwhile is difficult at first. If you keep at it, over time it will become easier and more natural.
With each harmful habit replaced by a beneficial routine, you begin to build confidence in your ability to effect change in both yourself and the world around you. You begin to look for more problems to tackle. Perhaps strange to say but you might even run out of problems and now are looking to make the good things in your life even better. Your improvements would be more impressive than mere arithmetic. It would be analogous to starting from being one foot tall to being five feet tall over time. Then if you continue to work hard, you will become six feet tall. You press on and work some more still, neither looking back nor comparing yourself to others, and pretty soon you find yourself seven feet tall. Who is seven feet tall in the world? Not too many people.
So when a person goes to you and say you are short, would you be upset or perturbed? Or would you simply smile and send him on his way? You can try to correct him of his obvious error but one would have to be ready to receive such instruction. From my experience, people who are ready and willing to learn, you cannot keep them away regardless. The more you try to discourage them, the more encouraged they are, since they realize you have what they need.
If you want to safeguard inner strength, be sure to build outer strength as well. Although your soul and mind remain the most important parts of your being, the rest of your body must complement them. Otherwise, the gods would not have given you a body for you to take care of in the first place. Build endurance by not allowing your body to be too soft and affected by hot or cold weather, for example. If you hear yourself complaining about the weather being too hot or too cold, stop yourself immediately. Build stamina by pushing your muscles beyond their normal limit ever so slightly on a regular basis. It should not be painful, but it should not be such that you do not feel the difference either. Never allow the body to dictate where your mind wants to go, and let it be like a trained and disciplined soldier always ready to receive a command.
In summary, take care of you and your life will take care of itself. When circumstances do not work out as planned, you would simply keep on trying like you would try on another pair of shoes since the previous ones did not fit. You would neither expect all shoes to fit perfectly, nor would you expect things in life to work out as you have wished. Therefore, with a strong soul, mind, and body, you would gladly accept the challenge of the way things truly are, not what you wished them to be. Yet you have too much respect to bet against yourself, that in time, what you wished for might very well be what you have earned and worked hard for. In the same way, and proudly so, I have placed my bet squarely on you, Epictetus.
"Do not tell people what they should do when you do what you should not." Musonius