How does Boxer try to use his reason when Squealer says there is “proof” that Snowball was Jones’s agent? Why does Boxer eventually say, “Napoleon is right”?

From the text:

"I do not understand it. I would not have believed that such things could happen on our farm. It must be due to some fault in ourselves. The solution, as I see it, is to work harder. From now onwards I shall get up a full hour earlier in the mornings."

Boxer cannot be critical of Napoleon, as he has been conditioned to follow.