With all the time we spend living in our heads, trusting all of our thoughts, emotions often emerge as more believable, and take control. Unhealthy behavior is the common result, and can usually be addressed with simple honesty.
It’s been said that “Denial is the ultimate comfort zone”, but “Unexpressed emotions never die. They are buried alive and will come forth later in uglier ways.” If you don’t rise up and possess your behavior, unhealthy behavior will continue to possess you.
Codependency is a kind of possession. Something besides your conscious mind is in control, and you are horrified of what will happen if you don’t feed it. That terror is what possesses codependents to rationalize unhealthy behavior like their lives depend on it.