"Do not be deceived: 'Evil company corrupts good habits.'"
There are many passages in the Bible that warn us about deception and rightly so as deception is a powerful tool used by the devil. When we are deceived, we follow a lie, which leads us away from the truth and as Jesus tells us in John 8:32, "The truth shall set you free..." Since the truth sets us free then its only natural that deception leads us to spiritual imprisonment.
If deception is so spiritually dangerous, then self deception is totally disastrous. When others deceive us, we are not fully to blame but when we live in a world of self deception, we are alone at fault. We decevie ourselves when we live according to the self. We trust no one but ourselves and ultimately love no one but ourselves and this goes completely against the will of GOD for us to depend on HIM. Self deception is even more dangerous as we don't realize we are being deceived. When others deceive us, we can realize their deception and correct it but self deception so clouds our judgement and waking up to admitting that we are deceiving ourselves is extremely difficult.
The only way to battle self deception, satan's most powerful tool, is to constantly run to Jesus and pray for guidance. Through faith in Him and relinquishing our belief of self reliance, we can overcome deception and live in His truth and we shall be set free.