I get this feeling quite often, I am a seasoned programmer who has stopped trying to learn everything. The result is a lot more space in my ram headspace for my life and family.
The downside of not knowing everything comes from the root of why I'm a programmer and not a math guy, I don't need to know the answer I need to know the question, this means I need x? To get result, but what is x called again? I used it last year, ummm it begins with R... And so on and so fourth, googling a few rough description to find leads for the name of the thing that I need. Is that you? I'm here to tell you that I have no answer for this, it's just part of being human.