I have written before about Dealing with Coding Insecurities including experiencing some feelings of inadequacy at work.
I have found this video to be an amazing counter to my coding insecurities: How To Fight The Programmer Impostor Syndrome?
John Sonmez explained some great points such as compare yourself to where you were one year ago, or to where you were 5 years ago. When you compare yourself to your past self, you can really see how much progress you have made.
Another great point was that if you are not feeling overwhelmed, then you are not challenging yourself enough. The goal is to get into tough situations sometimes and really grow and improve from the adversity.
Check out the video here: How To Fight The Programmer Impostor Syndrome?