From Epictetus, in Sharon Lebell’s excellent collection of his sayings, The Art of Living:

I spend a lot time with college students, and many of them invest a disproportionate amount of mental and emotional energy worrying about what they want to be.

What if, instead, they focused more on who they want to be, on the kind of character and disposition they want to mark their lives?

People of my generation, though, are mostly resigned to what they do. (It’s never too late to rethink that, however.) Yet, who you are matters much more than your job or your career path.

You have the power to make yourself into the person you want to become. Be clear about the kind of person that is. Envision your ideal self in as much detail as you can – habits, demeanor, character. Write down a description of that person. Keep it in a journal or in your computer or on your phone.

Read about people you admire. Seek out mentors and kindred spirits. Fill your mind with what you’re aiming for.

And start acting like you already are who you want to become. Live your way into the person you deserve to be.