Why did St. Peter deny knowing Jesus three times?

According to the Gospels, St. Peter’s denial of Jesus was not a result of a loss of faith, but rather demonstrated a momentary weakness of will, a tendency toward vacillation, and an inability to act under pressure.1

Prior to the event, Peter had overestimated his own capabilities, boldly declaring that he would rather suffer death than disown his Lord, even if all other disciples deserted him. However, when he followed Jesus to the high priest's palace after the arrest, he was confronted with the immediate danger of admitting his association with Jesus. In that moment of fear, he chose to deny knowing him. The depth of Peter's shame and his enduring love for Jesus were revealed when he realized the prophecy of his denial had been fulfilled and he wept bitterly.1