Just do it, the slogan says. So simple, it's a cliche. So simple, it's annoying.
However, sometimes one does not need to worry about "being" something as much as "doing" that thing.
In Buddhist thought, it does not matter what one professes or claims. There are no creeds to recite. Well, there are precepts, but my understanding is that if you follow Buddhist practice, that's all you need to do to be a Buddhist. No declarations necessary.
A writer does not need a book deal or an office to be a writer. Nobody hands out cards that will proclaim you or asks you for your credentials. To be a runner, you don't have to race or undertake a marathon, or if you do run a marathon, you are not required to show your time at the next meetup. To be a runner, you simply have to run.
To be an artist, one needs to create. One does not need an art degree, or the best materials, or a separate studio, or the approval of ones spouse (although most of that doesn't hurt, either). One shows up and does the work.
On the other hand, I myself did not always avail myself of opportunities and encouragement to become more. My professors encouraged me to apply for that grant, enter that show. It had not even occurred to me that I could do those things, much less should do those things. I didn't feel like a "real" artist, and therefor, what? So any little nudge was good. You could really do something with yourself. I didn't hear that one, or I didn't notice I had heard that. I was afraid to be ambitious.
But that's a different problem. When the idea of something intimidates one into doing nothing, that's a problem.
To be a thing is different than to be the person who does that thing. I'm thinking of writing, creating art, running. It's sometimes a bit like love. it is not enough to say "I love you," although of course, that is nice too! Some days, the feeling is not prominent, but it does not matter. What matters is that you act out of love, act in ways that express love, creating love out of your actions.
And sometimes being an artist, a writer, a photographer, is like that too. It's not enough to say "I am an artist;" what matters is that you create art. Well, sure, it can be powerful to claim those labels and say (declare/admit, depending on your feelings about it) that you "are" a runner, a photographer, a writer. But the label is not as important as the doing. You create your state of being out of your actions.
Be (act) the change you want to see in the world, as Gandhi said. To be the person you admire, it is not necessary to say "I am such-n-such." To be that person, act. To be that person, do. In the act of doing, one becomes the person who does.
Yes, I am an artist. I will occasionally admit to that. I am one who sees and creates, who conceives and creates. And so, I write. I photograph. I don't run; I hike. I used to paint, and shape clay; now I make dance programs and shape the flow of an evening. Yes, I have standards for myself, but that is not the point. I create the thing I want to be by doing. Or often, I do what speaks to me and the label finds me later.
Thus I write and find myself a writer. And for now, that is enough.