I usually take Thursdays off from work so I play a lot as a single paired with others. In my opinion, it is definitely the casual/occasional golfer that is the biggest problem. They haven't played enough to know or follow the flow of play and are not ready when it's their turn. When they're waiting their turn on the tee box they've got their face in their phone so they're not mentally prepared for the tee shot. Often they haven't even planned the tee shot when they finally step up. It seems so obvious to those that have been playing for decades but they really don't get it.
Since they don't play often they have a poor sense of where their ball might be on errant shots so they're often looking for it in places in can't possibly be. If it's a younger guy with some swing speed and a premium ball he might spend a full 5 minutes looking for it while the group behind stares with their hands on their hips. This is what really takes me out of my game: the group in front of us is over a hole ahead, the group behind is breathing down our necks and the oblivious guy in my group doesn't even notice or seem remotely concerned.
TLDR, it's the occasional golfer that is the scourge in regards to pace of play.
Since they don't play often they have a poor sense of where their ball might be on errant shots so they're often looking for it in places in can't possibly be. If it's a younger guy with some swing speed and a premium ball he might spend a full 5 minutes looking for it while the group behind stares with their hands on their hips. This is what really takes me out of my game: the group in front of us is over a hole ahead, the group behind is breathing down our necks and the oblivious guy in my group doesn't even notice or seem remotely concerned.
TLDR, it's the occasional golfer that is the scourge in regards to pace of play.