Judges 16

"If I am shaved, then my strength will leave me and I shall become weak and be like any other man" (v17).  Samson didn't really believe he was like "any other man."  Knowing Delilah had betrayed him three times, he still told her the secret of his God-given strength.  Perhaps he thought he'd awaken if she cut his hair.  Whatever his reasoning, he over-estimated his own power.  When God left him, he truly became "like any other man."

The scriptures, both old and new, warn against arrogance.  If we can't see our human weakness, we can't ask for God's strength.