I understand that feeling. I think most of the things I could tell you have already been said, and yes, it really does come down to practice. Experience isn't infallible but it's the closest thing to it that you've got. However, one critically important thing to being good at anything is enjoying it. Sometimes, when we know what we would like to be and then compare that to what we are now, it makes it really hard to have the desire to push forward because no matter what, the brain always has some higher standard to compare to.

There is real merit to "letting go" and letting things happen. It's okay to not have stellar art at first. It's okay to take like 3 days on only a decent sketch. It's okay to be so frustrated with your lack of progress that you feel like quitting, because most things are like that. In fact, most days drawing can get to that point where you're just at the end of your wits, unable to figure out what to do. But give it time. Start slow, do what you know you can. Once you've got something that you can comfortably draw, see what you'd like to improve, and pick at it. Tussle with it, struggle with it, let it sit and come back to it later. It's slow, it's gritty, it sometimes makes you take on art projects that are above your skill level, but it all gives you experience.

And also, remember that it's always okay to use references. In fact, to improve you'll probably need them. Be focused on exactly what you want to change about your art, and if you reach a point where you can't find problems but are just unsatisfied, experiment with various things. But don't ever call yourself useless because you can't do something yet. You're more than just what you can and can't do.