I think understanding the evil servant is a key here. First, the evil servant has in mind a specific time his master is due to come back. When enough time passes and nothing happens, he begins to wonder if the master is coming back at all. He then appoints himself master, and starts doling out discipline, 'beating his fellow slaves', that would have been reserved only for the master. The master gave him authority to feed everyone, but not to enforce the rules of the household or punish/be the judge of fellow slaves. His job was to do his job, not to make sure everyone else was doing theirs, otherwise he's an overseer, which is a bit different.
He can be pronounced happy if he's doing what he was told to do when the master arrives. What was he told to do? Feed everyone at the proper time. Was he told to rule in the master's stead, or create new rules and enforce them? No. Was he told to offer predictions from his own mind as to what time the master would get back? No. Was he told to use the master's resources to build really big houses for himself? No. If he bears in mind his position, he wouldn't even think of doing stuff like that. If he had authority to do that before the master came back, there'd be no need for the master to appoint him over all his belongings at the end! It'd be the equivalent of giving him what he already had!
So...there you have it.
--sd-7