It's a simple, but accurate statement. People do "what works" too. If you put a $1 in a vending machine and do not get a can of soda, would you keep putting $$ in that vending machine? No, you would find a machine that worked. Dogs will 'do' the behaviors that work - ie: gets them what they want. Which takes us to the next concept ....
What is reinforced will likely occur more often. What is not reinforced will likely occur less.
I like my job, but if I didn't get a paycheck every 2 weeks, I don't think I would go back. Would you? Even though I have been working for 40+ years, I still want paid for my 'work'. Pay your dog for a job well done.
THIS IS IMPORTANT - we are not here to trick or test your dog. We want them to learn, so let's help them in any way we can. I strive for Errorless Learning. The more successful the dog is, the more he will want to offer that behavior - WHY? Because he is being reinforced for correct responses.
When teaching new behaviors, frequent - almost constant - reinforcement is necessary. As the dogs learns, we fade the reinforcement to a variable rate - similar to slot machines. He never knows when the treat is coming. This is why the slot machines are very addicting - you never know when that BIG jackpot will come up.
Reinforcement is not always treats - it can be praise, play or the freedom to sniff.
Dogs do not generalize behaviors well. If you only practice sitting in the the kitchen, don't be surprised when you ask the dog for a sit in the family room, that the dog looks confused. You need to practice in all areas, inside and out. If only mom practices the sit, then the dog will only sit for mom.
THINK PAVLOV! Dogs are always making associations. Some associations are good and some are not so good. We can take advantage of this in training and make sure that the associations are always good. This is why it is important not to use aversive punishment's - i.e. Shock Collars. If the shock collar is associated with you, then your presence will predict pain - which in turn can lead to aggression.