Our psychological defenses have for the most part not been consciously erected. And each is there to serve some purpose, but often as we grow older their usefulness becomes questionable. Often they have arisen to protect us from forces which in some way threaten us. That could be due to a specific relationship, certain social settings, or from unconscious aspects of the personality which are thrreatening.
Rationalization, one of the seven defenses explored in the link above, often gets encouraged in subtle ways as our society has placed such a high value collectively on our ability to think. Creating excuses for difficult situations is on one hand an attempt to justify what is going on in our lives, but more accurately it is a maneuver which protects us from feeling the truth of our situation.
Regardless of the defense, it needs to be treated with respect. Seemingly impenetrable defenses can shift in unexpected ways when we are in a process that makes it safe enough to work with them. Like in the image above, an opening can emerge that will allow the waters of life to flow again.