When contractual relationships begin to deteriorate, the battle of the letters begins. A good letter will document the facts and circumstances, reference the applicable provisions of the contract, and may or may not suggest a resolution to the dispute. You are part historian, part journalist, with the overriding task of keeping your scope of work on track for the good of the project. Taking this approach usually takes care of the real reason you are writing the letter, whether that be to protect yourself or to convince the recipient to do something or stop doing something. Emotion has its place, but treat it like hot sauce. Too much will spoil the meal.
An astute documenter understands that his audience includes not only the recipient, but the judge, juror, or arbitrator as well. As a general rule, a letter loses something when the author’s disturbed emotional state is the focal point. Feel free to pour your anger and bewilderment out on paper, just don’t send it to the other side.
And declaring your emotional state doesn’t really address liability or fault. I am shocked, for example, when I accidentally hit my thumb with the hammer, disturbed when I open the cable bill, and outraged when I run out of coffee.