And the Lord said, Who then is that faithful and wise steward, whom his lord shall make ruler over his household, to give them their portion of meat in due season?
Blessed is that servant, whom his lord when he cometh shall find so doing. Of a truth I say unto you, that he will make him ruler over all that he hath.
But and if that servant say in his heart, My lord delayeth his coming; and shall begin to beat the menservants and maidens, and to eat and drink, and to be drunken;
the lord of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers.
And that servant, which knew his lord’s will, and prepared not himself, neither did according to his will, shall be beaten with many stripes.
Luke 12:42-28
Note that the only difference in the good servant going bad is that he changes his doctrine, he says in his heart “My lord delayeth his coming”.