Our Gemara on Amud Beis discusses the halakha that even a day-old bull is called a bull, and even a day-old ram is called a ram. 

Sefer Chayyim V’chessed (272) observes that this principle is based on the biological truth that animals tend to be born with all the basic skills and instincts they need to survive. In comparison, a human newborn is helpless and needs decades of instruction and modeling by his or her parents to develop the necessary skills of life. A human is not static and always potentially growing.

I believe there is a well-meaning but misinformed belief that seems to be repeated often by experts as if it were Torah MiSinai: “You cannot change your spouse.” And what I find even more troubling is that sometimes great rabbinic authorities treat pronouncements about personality disorders as if they were piskei halakha. Mental health diagnoses are highly subjective and two experienced therapists routinely will widely disagree about diagnoses. Additionally, the medical and pharmaceutical industry has a vested interest in describing as many human challenges as diagnoses and diseases, in order to promote medications and other medicalized treatments. However, although Chazal had a taxonomy of mental illness, such as Marah Shechora and Ruach Ra’ah (see some descriptions and sources in Eliyahu Rabbah OC:278), I doubt they would have considered personality disorders as a disease. They would call it poor middos.

While change is difficult, particularly deep personality issues, people still achieve change all the time if they endeavor to. Otherwise, why bother being alive? We are here on earth to grow, and a marriage relationship is a wonderful way to learn about our weaknesses and develop new strengths and abilities.

With the right amount of respect, encouragement, motivation and education all kinds of change are possible.  At first it may just be surface and behavioral, but in time, one can develop new patterns of thinking that come along with the changes, as one experiences the rewards and benefits of more adaptive functioning. Yet, of course, there are those who do not climb out of the self-generated trap of harmful, distorted perceptions and beliefs. Some hit bottom and wake up, but unfortunately others may not wake up in time and end up driving their loved ones away.