What does it mean to judge someone favorably?

When a person sees that his fellow has done a certain action, and it is possible to be in doubt whether his intention was bad or good, it is like two pans of a scale, one bad and one good, and one must judge him favorably and think that he intended for good and not for bad. But in a case where it is clear that he intended evil, or where he is established as one who is evil, obviously the intention is not that a person should force himself and think that he intended good.