This image is connected to dancing but you can substitute that word for literally any artistic skill that requires a lot of time and training:

Your ability to create good work is somewhat linear curve - the more time and effort you put in, the more you get out of it.
Your ability to
understand what is good and bad is a fluctuating cycle of peaks and valleys surrounding your ability's growth. There will be times when your ability to know what is good is LESS than your current understanding of how to make what is good. These are the cherished moments of discovery and learning, when you're breaking through a lot of barriers and feeling like you might be onto something. There will also be times when your taste will be much HIGHER than your ability to make what is good for your tastes. This is the real challenge, and where most people stop.
It's important to keep in mind that EVERYONE encounters it, and the only way to get past it is to keep making work even IF you think it's not up to your own standards. The only way you'll know how to make things that sound good is by making a whole lot of stuff that sounds bad. Don't give up!