I used to be really bad at quitting in the middle of things if I didn't like how it was turning out. Nowadays I'm a lot better at realizing "of course it doesn't look good right now, it's only half finished!" A good example of this lesson I saw recently was watching my mom repaint an ugly old dresser. Honestly, it was looking awful until she added the final coat of paint and put all of the hardware back on. Now it looks great!
For me, I think a lot of it chalks up to having a lot of drawing experience and knowing how to fix things. The more you practice, the more you know what works for you and what doesn't, and that will save you from a lot of "uuuggggh this drawing is so terrible I hate this" moments.
When it comes to comics specifically, I think it always starts out slow - especially if you're using a different style or method than you're used to. But the more you do it, the more you memorize your process and the quicker and easier things get!
So yeah, practice practice practice. Continue to build up your skills and you'll build up your confidence too! Of course, there are always exceptions. Even the best artists run into a peice that just does NOT want to be made!
Also, one more thing: Rebecca Sugar wrote in the Steven Universe art book that she was once terrified of sketching because it made her miserable when something didn't turn out how she wanted, but in art school she was forced to sketch and it made her be a lot more accepting when things turn out bad.
The thing is, to most artists, the majority of their work isn't how they want it to be. Rarely does something turn out EXACTLY how you hoped or imagined. Not every peice of artwork is going to be a masterpiece or be super popular, and it's okay to mess up and it's okay to drop a peice entirely if you're not feeling it. Artists are constantly improving and there's nothing saying you can't revisit a concept later on when you've got more experience under your belt!
Hopefully that makes sense and helps, I'm super tired so I'm sorry if I'm just rambling! XD <3