Someone who buys a bar of soap and never unwraps it will never become clean. A foolish spectator will attribute this person's lack of cleanliness to the "ineffective" bar of soap. The spectator will come to the conclusion that it is impossible for any person to clean himself with soap.
Similarly, a person who sees someone who learns Torah but acts in a manner that is dishonest will come to the conclusion that there is no redeeming value or truth in the Torah. He will come to conclusion that this fact exempts him for observing the mitzvos. He will never spend the time to "unwrap" the Torah and let its teachings cleanse his neshoma.
In both cases, the basis for subsequent opinions and actions is the person's own misperception.