"She said, 'The Philistines are upon you, Samson!' And he awoke from his sleep and said, 'I will go out as at other times and shake myself free.' But he did not know that the Lord had departed from him."
Over time and through many opportunities to repent, Samson had slowly but surely slipped into a spiritual stupor. With each link in this chain of sin welded by his sensuality, he had gradually become so unusable that he forfeited the Lord's blessing and empowering. Long before he would lose his eyes physically, he had lost his spiritual sight, his sensitivity to the Lord's activity, his usability in His kingdom work.
There is great warning here. Let him who thinks he stands, take heed that he does not fall (I Cor. 10:12). No one, however spiritually mature, is incapable of falling as did Samson. To think otherwise is to act the fool.