Usually after the six to eight month time frame the owner begins to expect the dog will follow through on commands, and perhaps begins to become a little less attentive to rewarding the dog for following commands. Gradually the dog becomes a little slower at sitting down, spends a couple more seconds sniffing around before coming back and maybe just gives one extra bark after you give the command to stop.
By not re-training or correcting these behaviors immediately you are actually teaching your dog that you don’t have to pay attention or that they can choose to listen and obey when it suits them.
Some owners even make the mistake of more directly rewarding their dog for bad behavior. This is most common with small and toy breeds that may fall into the spoiled dog category. When these dogs bark or snap at someone, the owner picks up the dog and actually pays more attention to it, rewarding all the possessive and territorial behavior.
Correcting problems doesn't mean using any type of punishment or harsh discipline; rather it means working on obedience and finding ways to reward the dog for doing the right thing. For most dogs this means combining food rewards, verbal praise and lots of petting and attention for the right behavior.
Using ignoring the dog when it does something wrong or a simple "No" or "Bad dog" and then ignoring is all it takes if the dog is bonded to you at all.