Prognosis after surgery

I have a question that may or may not have a true answer, but I can't seem to wrap my head around it (no pun intended, LOL).

I understand that surgical options are available as a treatment only and not a cure and that the surgery may halt progression or merely slow it down for a bit of time. With that said, If we have a decompression surgery and have the tonsils "removed"/cauterized...then how can symptoms still appear & progress?

I grasp the concept that any damage done prior to surgery won't neccesarrly go away, so I am not talking about having the same issues. I'm asking, how can new symptoms appear and how can those symptoms & the symptoms present prior to surgery progress and get worse?