We only see that they seem easily convinced and persuaded by these lies because we know that Edmund is a treacherous villain and that Lear's two daughters. Goneril and Regan, are greedy, selfish women who have no love for their father but have been practicing telling him lies all their lives. Edgar, Gloucester and Lear do not have this inside knowledge; they love the people who lie to them and betray them and assume that the love is reciprocal. It is easy to deceive people who love us and easy to be deceived by people whom we love. Edgar, Gloucester and Lear are not naturally guilible, but they are not naturally distrustful of all humanity. (Lear ultimately becomes disgusted with humanity.) Only the Fool has a thoroughly negative opinion of humanity, and we can imagine how such a unfortunate person, a village idiot, must have been abused by everyone from childhood up, until he was adopted by Lear. One of the main themes in the play is that true love is a lot more rare than most of us would like to believe.