And his arrogance increased as he never thought it his wildest dream that what the apparitions said to him would come true, specifically the prophecy about "no man born of woman will harm MacBeth." So when he heard about Birnam Wood approaching the castle he wasn't concerned. However, we know that pride was before his crash when he learned what that prophecy really meant for him. Even then MacBeth thought he could outwit was was already forordained for him.

At first, Macbeth feels confident that no harm can come to him unless the prophecies of the witches come true. He has no fear. He's playing the part of a despicable tyrant to everyone around him. Those who still serve him do so out of fear rather than loyalty. He's arrogant, calling his servants cowards, and he considers the opposing army to be lazy and self-indulgent. He appears to lose courage temporarily after he's told a large army is approaching, but then he dismisses the news, just as he dismisses the news of the doctor concerning his wife.