The sane writer (whether of books and essays, or a singer/songwriter, or a playwright, or a poet) learns to thrive on internal validation, and understands that creative output is a God-given gift and right, not a gatekeeper-dictated privilege. It is not dependent on age (in fact, most bestsellers come to authors over the age of 55), it does not favor youth and innocence, and it need not stop if one gets what some people love to sneeringly call a "real job." Wallace Stevens was an insurance executive. Rita Mae Brown was once a bricklayer. (I've always found that really cool.)
If I could impart one useful phrase to everyone who visits Booklab discouraged over rejection, it would be this: "Who are these people?" Submission is often necessary, and I believe in heeding wise agent or editor counsel, but submission does not overturn the essential authority of you as an author. You're the one who chooses when you start, how you progress, when you stop, and -- even if it has been decades -- when you start again. No other person -- parents, teachers, mentors, employers, agents, editors -- controls a bit of it.
I guess this is the part of the post where I sum things up in a pithy way, and then add an image about perseverance. But I'm feeling too contrary for that. After all, some people really aren't good writers and never will be. Yet who am I to decide? I can think of five or six people on the bestseller lists right now who write books that I find problematic in the extreme, with issues ranging from poor writing to "ew" subject matter to aimless execution, and I can name a host of wildly talented people who aren't published and possibly never will be. Far be it from me to say your good work will prevail in the traditional submission process if you are diligent. Maybe it won't.
But you still get to decide. It's still your life and your ride. And if you silence yourself because you didn't get one over in an arbitrary, power-laden process called submission, you may deprive me and others of your breakthrough work.
Here's an interesting quote from Spike Lee when he learned that Barack and Michelle Obama went to one of his movies on their first date in Chicago: "Actually, Barack told me the first date he took Michelle to was Do the Right Thing. I said, “Thank God I made it. Otherwise you would have taken her to Soul Man. Michelle would have been like, ‘What’s wrong with this brother?’ ”
Lee made that movie, and all the others, without asking anyone for permission. In fact, Lee never really participated in the submission process as it is traditionally defined. Read his bio here, and you won't see one word about how he offered his work to someone else and silently begged for validation.