After Napoleon announces that he will be the deciding voice in any debate, and that the pigs will now make decisions without the input of other animals, some feel that this is unfair. After the dogs menace some dissenters (showing the use of military force to quell sedition) Squealer goes to work, using outright lies and the power of propaganda to convince the other animals that this is Napoleon's way of taking the hardship of decision-making on his own shoulders:
"...Surely, comrades, you do not want Jones back?"
Once again this argument was unanswerable. Certainly the animals did not want Jones back... Boxer, who had now had time to think things over, voiced the general feeling by saying: "If Comrade Napoleon says it, it must be right." And from then on he adopted the maxim, "Napoleon is always right," in addition to his private motto of "I will work harder."
(Orwell, Animal Farm, msxnet.org)
Boxer, who represents the undereducated working class, believes in his leaders to make his own life better, and believes that his hard work will eventually pay off. However, here he shows that he is unwilling to argue with the bad decisions of his leaders; by claiming that "Napoleon is always right," Boxer opens up his future to any decision made by Napoleon, and loses the right to question the process. This addition shows the ability of people to voluntarily enslave themselves without realizing it.
"Napoleon is always right."
The other motto is "Napoleon is always right." This can be found in Chapter V (5) page 40.
"If Comrade Napoleon says it, it must be right"