"harmonious nature of existence" entails that the Basis of existence is non chaotic.* There is ontological truth for everyone, some people simply disregard
what is true but that does not necessarily change what is true.
There is a 'dissonant nature of existence' that exists and holds just as valid and 'real' as the 'harmonious nature of existence'. Hunger for example. This would entail that parts of the world are chaotic. Since chaos cannot be organized, but temporary organization can be produced through chaos, it would be safe to say that the dissonant nature of existence is of considerable equivalence.
I guess the truth that exists for me contradicts what I consider truth.
These people are not exceptions but simply "divergent" from the truth, depending on that degree of the divergence one might find what some call insanity.
So the farther away we get from believing that 'there is a harmonious nature of existence (while disregarding the dissonant nature of existence) the more we are 'insane'?
Life is beautiful, life wants to experience this beauty. If life was not harmonious then there would be no attraction to being thus there would be no life.
There are plenty of people that I met who don't regard life as beautiful, thus wants to experience escaping the dissatisfaction of life, or coming to terms with the fact that life is not beautiful. They are still living, their attraction to being is not attraction to actual 'being' but 'being within certain states of mind.'
People who commit suicide, kill, ect. are not exceptions they simply are unaware or aware but still disregard.
"Life is so beautiful, but I'm going to disregard this and kill myself?"
My argument to this is similar to that of the people who commit suicide this is not an expectation but a divergence. But in this case the degree of the divergence is not so directly related to the death. (that is good news for you)
Even if this was the case, it still shows that their is a equally or at least a significantly dissonant nature of existence as well.