Chances are, you didn't have to learn how to be hard on yourself. As your own greatest critic, only you know what those moments when you're left with only your own thoughts in solitude are like.
By nature, I'm a pessimist. I tend to invest a great deal of time imagining how and where things could go wrong. I've, admittedly, allowed these thoughts to consume me—to cripple me from taking chances or from fully enjoying the here and the now. Being aware of those tendencies in myself has enabled me to find my own workarounds for dealing with them. I've set up my own safeguards for pressure testing these internal dialogues and rooting out the valid concerns from the illogical ultimatums.
With the demands of a full-time job where creativity means more than just showing up, you're liable to experience dry spells or days where you're not feeling particularly innovative. There are projects that will pass you by that didn't meet your expectations for how you could have pushed yourself into new, unreached territory. These feelings are natural and, in and of themselves, aren't harmful things to think about. They're a great gut check for being aware of your own strengths and weaknesses. In equipping yourself with an insight into your own flaws and shortcomings, you can better prepare for future projects and interactions—pinpointing your more troubling proclivities.
All around us, there seems to be an unrelenting chorus that tells us to "do better". They tell you to expect more of yourself. Demand it, even. To not allow yourself to be content with where you are. As an internal mechanism, these tendencies can propel us into new, uncomfortable areas of our careers. Occasionally living in this tension can be a shot in the arm of complacency. But I'd strongly caution you from allowing these voices to dominate your professional or personal attitude. Self-deprecation, while maybe jolting in the short run, doesn't have the stamina to be all that fulfilling on a large scale.
Figure out how to think critically about your design decisions. Get informed about yourself and learn how you can more effectively live in the tension that exists beyond your comfort zone, but do so without allowing it to consume you.
Try not to be so hard on yourself.
Even you deserve a break from time to time.