It can strain you mentally but in general all of my portfolio has been a success aside from one. 

That is a home owners mentality.

I have to be comfortable renting to the people that live in the area (I don't care about race, family type, sexuality, I'm talking about the war zone personalities/mentalities).Anything that meets to above criteria I want to keep as a rental.

I also have partnered with the local county programs for adult mentally handicapped tenants.

I look back at it as a great decision.Selling it cut my looses in a declining marketIt was a mental relief to get rid of the problem.

My stress levels went way down and I feel so much better physically and mentally.

The top employer is the University of Arizona which fits with my rental strategy to possibly rent to faculty, graduate students, or professional students.

Although he is likely mentally unbalanced he will simply move since all his threats are posturing in a attempt to intimidate, and seems to have had a effect.Get rid of him asap for the sake of your tenants.

If you're going to continue to be under pressure mentally and financially you will never be able to get to 14 but if you go to 12 and go back to having no consumer debt, 14 is easy. 

His mistake was he went alone and he was dealing with a mentally imbalanced tenant.