Can I start by telling you that, whatever you dream about doing, if you're willing to put in the work, you can achieve?
Being a writer can be a lonely, difficult, and depressing life. There are days that the words come and you're sure of what you're doing. Then, there are days where you honestly look at what you've written (or even a blank page) and as: "Who am I kidding?"
This happens to all of us. It also happens to pretty much anyone who does any kind of arts: dancers, musicians, actors, artists, poets...etc. If you do something that has to do with creativity or creation of any kind, you will feel this way at some point.
Part of this is just our humanity and worry that in some way we aren't good enough at what we love or that the thing we love is about that passion and in no way about skill. It's rough and for many people can hit you hard enough that you sometimes get up and walk away from what you love.
Stop. Sit your ass back down and listen to me: Nothing worth your hopes and dreams will ever come without blood, sweat, and tears. No one is perfection straight out of the gate. No one with any skill can continue to be that way without putting in hard work to improve and hone that skill.
Look at a professional athlete: Have you ever heard one tell you that they don't work hard at what they do? Have any of them said, "I don't practice or play other than at the games. I spend the rest of my time sitting on the couch eating junk food and thinking about how great I am." No.
You may have a gift or you may choose your path based on what you want. Either way, it takes dedication to ever be successful and you will doubt your self/sanity at times. Sometimes you will yearn to be at the top of your dreams with a painful clutch in your chest and think of all of the reasons you aren't there already.
Don't waste your time. You are enough. Your dreams are achievable if you focus and tell that damn voice to shut the hell up. Do the work. If it's with writing, then sit your ass down and write until you fall asleep at your keyboard. Give yourself goals and then crush them. Find a carrot to dangle so that your daily word count is where you want it to be.
Remember though: Nothing is perfect the first time. The hardest part about anything you do in life is taking that first step. As a writer, it is putting that first sentence down and then the second and then...all of it. You will struggle and falter, but you get right back in there and you do it again tomorrow. You are worth fighting for, so fight. Screw that voice that tells you otherwise. If you want it; be it. Stop wasting your time with failure and start winning your success.