The key to a successful working relationship is the partnership. You have to start over with each dog because you don't just spring out of the box with a talented dog automatically in partnership. You start with a (hopefully) talented dog who just wants to control stock and you have to get yourself into that picture.
There does seem to be not so much a moment where you decide to trust your dog, but a gradual development of trust between you and the dog, on one hand that the dog is going to do the right thing, and that he's going to at least give consideration to everything you say- that he's listening for commands because he believes that you are helping him to do the job, not that he's listening for you to get after him about something and will obey because you will make him. You do have to start out that way, because if you aren't able to make him listen, there will not be a partnership developing. You also have to know when to give him a chance to try things out and not constantly command or correct. If he's a good dog he wants to be right and will learn from things that didn't work. Your goal is to try to set up things so they will work most of the time and he won't be frustrated by work that is too hard for his level of experience.
It comes in certain moments, whether they are at a trial or at home getting a job done, and is very much like flow. Flow is a concept of being fully present, in tune with your environment (dog and stock) and everything is just clicking. The more moments you have like that with your dog the stronger the partnership is until it can feel like the dog is almost an extension of you some days. You are reading his thoughts and he seems to be reading yours as well as reading the stock.
This is more than mysticism, it is being present, knowing your dog and how to read him. It doesn't come from thinking or wishing or watching other trainers. It comes from using your dog to accomplish a job time and time again. It comes from work.
A couple of examples follow that stand out as being such moments to me.
Yesterday, I used Hank to sort the sheep for feeding as I do with one of the dogs every day. The ewes are getting extra grain to fortify their advanced pregnancy. The other sheep, mostly wethers, also would like grain but don't get it because they are on a hay diet. I held the gate, watched the sheep and gave commands to Hank to hold back the wethers and ram while I let the ewes through. He did his part and I did mine and it took about 5 seconds to finish. With a less experienced dog I probably would have futzed around for minutes with it, perhaps getting smashed against the gate by sheep, or letting the wrong ones through.
Last fall at Sprite's first trial, on one of our duck runs, we had a difficult group that was determined to split and do a double end run around us to get back to the pens. Without really any command but "there", Sprite took charge of one side and I took charge of the other and we worked the ducks across the pen toward the obstacles. It ended up being short of qualifying but it was one of the high points of the trial for me because of the feeling of partnership between us.