All the time. I deal with almost constant anxiety over how my time is spent, even to the point where I can't always enjoy leisure activities. I don't know what drives this. I am not an overly competitive person and already have a decent job where people respect me and my abilities as a programmer, yet I rarely spend a waking moment not thinking about all the things I could be grokking.

I guess what it boils down to is that a lot of my self esteem is derived from being knowledgable and resourceful. It really embarrasses me when I don't even have a shallow depth of knowledge about a subject matter that could be potentially useful.

I don't really have much advice for you because I haven't really solved this one for myself, but one thing I try to do is concentrate on very short term goals. For example, when I was learning Angular a few years ago, I knew going into it that I wouldn't "get it" right away. After a few frustrating days I decided to break-up my learning into small goals, e.g. "what are promises and how do they work?" "What is the syntax?" "When should they be used?" I tried to avoid unrelated documentation and stack overflow posts because I knew that it would lead me into rabbit-hole after rabbit-hole. I wasn't 100% successful, but it did help me block out some of the cognitive dissonance.

The only other thing I'd say is that even though this is frustrating, I like to think that your anxiety is actually a good thing if you learn to channel it constructively. It's a good thing to want to know about a lot of stuff!