Shivas, endless preshot routines definitely slow things up, but I see them more as a symptom than a cause. Fast or slow, pace is a state of mind.
Faster players generally realize that a brisk pace as an integral part of enjoyable golf. Plus they are polite enough to try to avoid inconveniencing their fellow golfers. So they dont develop inordinately long preshot routines.
In contrast, slow players paid there money and will play at whatever pace they like. Never mind the 160+ golfers who may be waiting on them.
For a good indication of who plays fast and slow, hang out in the full parking lot of a crowded course. When someone is waiting for their parking spot, a fast player will get done what he has to get done (shoes off, bag in, etc.) and then get out of the way. Not hurrying but not wasting time either. In contrast, a slow player will somehow manage to take even longer than he usually would to exit the space, as if to prove that they are in charge and will act when they damn well please.
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I do agree with one point though, we all think we are faster than we are. After I recently commented on our recent slower rounds a few regular playing partners said that one of the reasons we were playing slower than usual was that I was hitting more shots and spending more time looking for more balls (my game is Duvalling.) On reflection I realized they were likely correct. Not much immediate I could do about the number of shots (I tried to move to up tees but to no success) but I did swear off playing any ball which cost over $20 a dozen until my game improved. My game hasnt improved much but my pace has.
My point? We could all probably use a little critical self-evaluation when it comes to pace issues.