You can read Part One and Part Two if you missed them by clicking on those links.
I think it is important to know your horses limitations and which battles to avoid with your horse. There are things that you may chose to avoid confronting with your horse, due to a variety of issues that may not come under the heading of enabling.
For example, Pippi can not be clipped. We tried for a year to desensitize her to clippers, and made some headway on her legs, but a bridle path or her face was out of the question. When she had some teeth work done, we decided to take advantage of her drugged state and try to clip her bridle path and muzzle. She walked two people out of her stall, and just about came unglued. It was at that point that I said "enough!" We can use scissors, and bikini shavers and I was no longer willing to fight this battle, potentially hurting her and us. (I could go into all the ways that we tried to work with her on this, suffice it so say we tried it all (daily) for over a year.)
What I mean when using the term "enabling," is when someone allows their horse to not handle routine things. Things that they should, and quite frankly has to in order to be a safe horse, handle, but their human shelter them from. Pippi not clipping does not affect anyone but her and I, and it puts no one in danger. (Clipping her does!)
When you take your horse to a show, or a clinic, trail ride, whatever, there are certain things that your horse should be able to handle. Routine things like another horse being lunged (with a lunge whip), trucks and trailers being moved around, horses coming out of those trailers, music, announcements, horses being worked in arenas or running in a field, people yelling and making noises, horses being hosed off, water buckets being filled and dumped, wheel barrows, etc etc. This is all routine horse show stuff. If you have a young horse, they will be nervous and perhaps a jumpy mess, but sheltering them does not help in the long run. Instead, it is important to stay calm, and let your horse get used to it.
If you go on a trail ride, your horse must cross water more than likely, so if you don't want to tackle that, don't go.
When it rains the arena will be sloppy, make your horse deal with it, or go home. Do not ask that the clinic/show/whatever be moved inside because your horse doesn't like to get dirty. (Pippi is a Princess, so this would be a battle for me)
They will announce you at a show, deal with it! Do not ask the show not to announce you and your horse because it bothers the horse, you are not the Queen of the Universe, and your horse will never get over it unless you deal. Stand close to speakers leading up to your ride, and your horse will get the drift. Or not, either way, you decided to go to a show and they announce stuff there.
Do not ask other riders to stop clipping their horse in their stall next to yours because your horse (Pippi) is afraid of the sound. Instead, ask that they stop for just a moment so that you can remove your horse. Go for a walk perhaps? It is your horse that has a problem, so your horse has to go, not theirs.
If your horse kicks out at other horses when they come close, put a BIG red ribbon on its tail. Sure, people should always keep their distance, but since your horse is the "aggressor", how about you give a reminder to the other riders? It doesn't mean that your horse is mean, it means you are a considerate and responsible equestrian. I am considering one even though Pippi has not kicked out (she pins her ears a bit), just because I think people ride too close and I would hate to get anyone hurt.
Do not expect horses stalled near you not to be fed whenever. Sure, your horse may have a conniption because their neighbor is eating. Throw yours some hay and teach your horse to deal.
Other people will lunge their horse with a whip, and they may even crack that whip. I don't mean, Indiana Jones style, whipping it around like a lunatic, or hurting their horse, but just your every day average lunge whip style. You know: Trot! 1-2-3 and Swoosh/crack whip, to get desired reaction from horse. Your horse is out in public, and should be able to handle seeing another horse being lunged with the accompanying whip. If it doesn't, you need to go home and desensitize this. Another option is to ask the other rider to stop "cracking their whip," which will at some point or another result in you pissing off a person who has shown admirable skill with a whip. I wouldn't advice it!
By not insisting that your horse deal with these type of things, you are enabling your horse to not learn and grow. Dealing with these issues is not just better for you, but it helps grow your horses self confidence. A horse needs to learn to do its job regardless of what average stuff is happening around them.
Pippi, for example, needs to stay on the bit even when a fly is buzzing around her face. She needs to learn to keep her attention on me, even when a trailer is being unloaded directly beside the arena (with great parking nearby I might add - aaargghhh). She needs to pick up her cues, even when a horse is running at a gallop on a lunge line in the next arena.
And if I for some reason chose to enable my horse, like with the clipping, it is MY problem. You should NEVER EVER EVER ask another rider to help you enable your horse by asking them to cease doing their normal behavior. You are in fact not the Queen of the Universe, and the world does not revolve around you and your horse. If your horse can't play ball, or needs the rules changed to accommodate their issues, go home and start your own league. Or go home, work on your issues, and try again another day. "Bomb proof" horses became bomb proof not by running for shelter, or asking the bomber to stop, but by learning that the sound was not in fact an explosion.