They sometimes don't even realize they're being unfair. They're way too stressed out and prone to lash out without thinking. They need to step back from themselves, and learn to relax..not jump to conclusions, be more open-minded and put themselves in the other person's shoes.
It all comes down to mindset and mental attitude. Can you change that? Of course you can..any thought process can be changed..the mind is very flexible..it just takes time. Of course if drugs or alcohol are involved it takes even longer.
Oh yeah..and they need to become a good listener too