What is the undergroundman?

Notes from Underground: A book about a man constantly battling himself -- and losing.

He falls into a small set of people who always know how they should act, but do not periodically act in that way. This distinction between knowledge and action is said to produce free will, and those people who know right but act wrong are thought to be morally responsible for their actions.

"If I know what is right, I can act right is" is apparently the syllogism with which which we judge people daily. In other words, all people who know what is right can act right. But doesn't that fly in the face of all empirics or logical sense? (By the way, I say only those who know -- what of sociopaths? Do they know the sin of murder any better than a cat knows the sin of murdering a mouse? What if a sociopath's brain is significantly different, as it likely is?)