How do I know if I’ve increased difficulty too quickly?

If your dog is engaged in the game and having fun, then the difficulty is probably good or could be increased. If your dog loses interest in the game, is stress yawning or barking a lot at the toy, consider decreasing difficulty. Some frustration is ok and is part of the learning process. If your dog is showing signs of frustration for more than 4-5 minutes, consider reducing the difficulty or taking a break for a few hours.