work in an open office with no dividers.
Unfortunately for me I don't have selective
hearing, so 95% of the time I'm trying to
drown out the buzz by wearing over-ear
headphones (usually with no music playing)
My wife has the same problem (no selective hearing). And while I understood it intellectually, it never really made sense. Of course you can focus your hearing, you just have to try... never said that, but that was my thought.
Then recently, an odd combination if sinus infection, cold, and related ear troubles inflicted this on me. I was attending a company/community even with several hundred attendees. Quite suddenly, it was like every conversation in the common area was happening right next to me. It didn't matter how close or far, or how loud - it was all happening at once, and I while I could still hear the person I was talking to, I could no longer distinguish what they were saying as there were too many other conversations that my brain was trying to interpret. This went on for about two hours, then my ears popped, and things were roughly back to normal.
Ho-ly crap. Even with that experience, I find it difficult to fathom living with that nonstop - I don't know how you do it without going insane, particularly if you have to work in an open office.
TL;DR: I finally understand the experience of lacking selective hearing, and sympathize. While hoping it never, ever happens to me again.