Imagine the following scenario: You have gone through all of the stages of engagement and are now working your dog at stage 4; your dog has opted in. You believe that your dog is well acclimated and clearly has asked to start work. You send your dog to fetch the dumbbell, and after picking it up, you notice your dog looking off into the distance or even heading in a new direction, and it's not towards you! Basically, something interesting caught his eye, and he'd like to go check it out. He's curious and not worried. Should you call your dog back to finish the exercise? Most of the time, yes, that is exactly what I would do. I do not want my dog to develop a habit of starting an exercise and then wandering around, so I will encourage the dog to come back to me and finish the exercise. This would be an example of removing choice from training. The dog chooses when to start work, but I choose when it ends. Once the dog has opted into work, and I believe that the dog is truly capable and ready to be there, I will ask them to push through for a few more seconds, even if it would not be their choice at that moment. My job is to pick appropriate environments and work that will allow the dog to succeed as much as possible. I also watch my dog's behavior carefully. If I can tell that my dog is working, but that part of the brain is not with me, it's fairly likely that I will end work very quickly and release them. What I don't want is for my dog to release themselves. If I do otherwise; if I allow the dog to wander away and come back when they are ready, then I am communicating to my dog that I find their choice to come and go acceptable. It's a bit of a have your cake and eat it too situation. And I don't find that acceptable! Once the dog opts in, I need them to finish until they are released. However, because I do not work with dogs that are not truly in the game with me, it's not likely that I would start a new exercise if I thought the dog wasn't really engaged. What happens at this point is more complicated and is extremely dog dependent. I may well release the dog to investigate the thing they want to see AFTER they finish the exercise, especially if it is a more fragile dog or a dog that I know will become fearful or shut down if they can't see the thing and reassure themselves that all is well. Or maybe I would release the dog to take a break without getting to the thing that has their attention (leashed or somehow controlled) and wait for the dog to restart engagement and work. Or maybe I know that it was just a weird momentary lapse, and now that the dog has been reminded of what we are doing together, we can continue as if nothing had happened at all. As always, it depends on the dog and the reason for the loss of attention in the first place. Curiosity, fear or boredom? Sturdy or fragile temperament? Experienced or novice dog? Those are the factors I'll consider when making my decision. If you are not sure what those terms mean, consider purchasing my book, "Train the dog in front of you".