Quite often, handlers assume that because their dog has been performing an obstacle that it really understands the purpose of the obstacle. That isn't always the case. This is where a lot of dogs will start shutting down as you add sequencing and raise the criteria. Why isn't your dog offering the behavior you desire and how can you encourage your dog to want to offer the desired behavior. Chris and Jeff Bolton from England also recommend using the leash frequently, liberally, and throughout the dog's career.
Attention is a two-way street.
If you are easily distracted when working your dog, don't expect your dog to pay attention either. Teach a million stupid pet tricks. They also promote a sense of teamwork between you and your dog. People who intend to compete in dog sports should not sit quietly by and let their older dogs be the sole entertainers of their puppies. When you get a new puppy, sit down with it and see exactly how people-oriented it is.