Having the sense you are good enough and awareness of what makes you feel nourished in all other areas.
Not believing in yourself is more common that you might think. Most people have self-doubt and can feel that everyone is better than them. This could be because of negative self-talk bullying you, which is now the norm. You might not even know that you do it.
To find internal nourishment you have to become self-aware, notice what makes you feel good or bad, what excites you, inspires you, gives you that sense of "this is what I am here for."
It also comes from taking the time to be with you, not trying to distract yourself with phones, TV, film, porn, eating, sports and family.
Just sitting and watching your thoughts and stepping outside of them.
By doing this you see who you are and who you can become. You are more than you believe you are, but are trapped by what you think or have been told you should be.
Being comfortable with yourself is how you find internal nourishment.