Is there a word or short phrase used to describe being impressed with someone's accomplishment while also clearly expressing a lack of understanding?
Depending on what their achievement was, the phrasing could be a little different, but I would use the word "Unfathomable" here.
It does a few things:
- Shows that you don't understand
- Compliments them by implying that they achieved something that is very difficult
- It's kind of a fun over-exaggeration (though I guess this could be interpreted as facetious to a stranger, if it is a friend I think it works great)
So maybe something like,
Hey ____,
I just wanted to drop a quick congratulations--
I heard about your _____ award, I can't even fathom how you did it, it sounds amazing!
I'm not well-read in what is proper English or grammar, I just stumbled on your question and thought I'd add my own personal answer