As in many other Greek plays, Tiresias speaks with a knowledge beyond normal human ken. He is aware of the will of the gods and can speak accurately of the future.
Just as he warns Oedipus what will happen if he follows up on his plans in Oedipus Rex, Tiresias appears in the last play of Sophocles' Oedipus cycle to tell Creon that his hubris will be his downfall.
"The blind prophet Tiresias tells Creon that he has angered the gods and that Creon is to blame for the people’s prayers going unanswered.[...] Tiresias calls Creon a tyrant and warns him that he will lose his son" (eNotes).
It is stubborn pride and a will for power that keep Creon from yielding to Tiresias' advice. The prophet identifies this as the principal source of Creon's failing, saying "[A]ll men make mistakes, but a good man yields when he knows his course is wrong, and repairs the evil. The only crime is pride."
Although Tiresias points to two practical mistakes that Creon makes ("burying" Antigone before she is dead and refusing to bury her brother), it is Creon's willfulness - his hubris - that stands as his central error. This error of character is within Creon's power to acknowledge.
Unlike Oedipus in the first play of this trilogy, Creon is faced with a choice regarding his future. Oedipus was only given a choice between ignorance and knowledge. He proudly chose knowledge and suffered that pride. Creon's choice is, perhaps, more immediate and simpler than what Oedipus faced. Thus his failure is greater.
His punishment is also greater and might be seen in connection to his political motivations. Creon asserts his rule over that of the gods and his family dies as a result. Oedipus' family was devastated, but his children survived his tragedy (initially).