Here in the PNW I've had new fly fishers tromp right in the water below me, walk and splash and fast as they can out to waist deep, and scare every steelhead that was lying there out of the run all because they can't cast more the 45' and think that they have to be waist deep to "get to the fish". This is very maddening because in another 40' of cast and step (as steelhead and atlantic salmon fishers cover the water) I would have been covering that water and the steelhead that used to be in it. Even more maddening is the attitude of the dude who low-holed and scared the fish in this manner when he is informed of his breach of stream etique and why he should have either started above those ahead of him in the run or waited his turn to avoid scaring the fish. The all-too-often response from the new guy is "this is a free country, the water belongs to everyone, you are a snob, etc.".
Another all to often scenario here in the PNW is the new fly fisher jumps in the water 150' below you and then parks there instead of moving downstream a step or two after a 2-3 casts. This causes the experienced fishers to move down in the step and cast, step and cast that is the most efficient manner to fish a steelhead run until he now has his casts running the risk of foul-hooking the new guys line or fly. Upon being asked if he would move down a bit, the new guy far too often ignores the request or says the same inane "the water is free, this is a free country, I'm just out for a day's fishing and don't appreciate your hasseling me, etc." Then to add insult to injury, when you move downstream of the new dude, he gets all huffy and angry that you are fishing "his water" despite the fact that he hasn't moved in the 45 minutes he has been fishing. And all too often as you draw near him from above, he starts giving you the look and many time says something about you crowding him and that you should go elsewhere if you can't respect another angler's "fishing spot".
Also, many time the new fly fisher will wade out to where you are casting, instead of waiting until you are finished fishing through the run, just to "chat" and visit. This is also very maddening since he almost invariably stands in the way of back casts or D Loops, chatters along while you are trying to concentrate on your fly's progress and how it is fishing, and in general just gets in the way. If the new guy would simply wait until the experienced fisher is finished fishing through the run before he starts talking to him, the experienced fisher would visit and be pleasant. However, when the new guy wades out and disturbs the experienced fisher, the experienced guy is less than happy, gets a little peeved at the inconsiderate actions of the new guy, and wants to get rid of him as soon as possible.
Likewise on a public spring creek when a new guy walks right up to the stream and scares every trout in the pool that the experienced fisher just spent 20 minutes sneaking up to the water's edge to cast to the fish without spooking them. Or the new guy slaps the water from the other bank with his casts and scares the fish that the experienced fisher has been working to catch for the last 15 minutes.
This is the stuff that OC was talking about. And the only way the new fly fisher learns how to do these things with consideration and fish and cast with skill, is by starting on easier to catch fish like sunfish and bluegills before he goes for steelhead or spring creek trout. Even the world's greatest guide cannot teach a newcomer how to cast 80' on steeelhead river in one day, nor can a great guide teach a newcomer how to make very gentle casts of 50' on a spring creek in one day.