"The More you know, the more you don't realize you don't know."
When I was a teenager and playing music everyday, I would go in monthly or quarterly cycles of confidence and insecurity in my playing. It went like this:
I would learn something that would open my musicianship up. Usually a new scale, a musician I had been listening to, or a new technique. This would turn my world upside down for a week and I would practice it over and over. After a couple of months, I would have the technique down pat, thinking I was pretty hot stuff. Then all in one night it seemed, my ears and brain would catch up to each other and I would be devastated that I wasn't good enough. This depression would turn into a quest to learn more and to get better. And this cycle went on for years.
This applies to much more than music. With anything that you do, there are going to be cycles. The longer I have a business, the more I learn and the more I realize I don't know which inspires me to learn more.
Learn something. Practice it. Get good at it. Let it soak in. Realize there is so much more that you don't know. Repeat.