Thoughts are powerful, whether they are positive or negative.
For me to realize, that it's not my mind that creates the feeling(s) in me, it's my thought: its what I tell myself upon encountering the stimulus: Upon encountering the stimulus, I tell myself, I don't like what I have encountered. Consequently, I make myself angry and then I throw my anger verbally at the other person with the intention of hurting him emotionally, whether I hurt him emotionally or not, but one thing is certain that I have emotionally hurt myself with my own anger.
Now I can say, stimulus is never the cause of my anger, the cause of my anger is my evaluation. Evaluation is a causative factor in most of our problems and single most important factor in breaking people apart. When the evaluation of a situation or evaluation of a person is positive I feel happy; when the evaluation is negative I feel unhappy. I can't get the unhappy thoughts out of my mimd, because I am thinking badly about the situation. No one can hurt me, except physically. Psychologically, I am hurting myself with my irrational thoughts. "There exists nothing good or nothing bad but our thinking makes it so". Shakespeare.
So, in reality, I am the one who is making myself angry and hurting myself first. In other words, what I do to others, I do it to myself first. Most people are not aware of this fact. This is Saeed's aim to make you aware of this fact. People can hurt you physically but not emotionally. Emotionally you alone hurt yourself out of your own negative evaluation / thinking. Emotions are our own inner matter to attend to and deal with. Think about this intelligently and compassionately.
Another example: I see the object and I feel the emotion. I feel the emotion, because I don't like what I am seeing and as a result, I can't stand that person. It is my own thought that says 'I can't stand him' and makes me angry and not the person (not the stimulus). The other person is not the cause of my anger, it's my own negative thought about the person that makes me feel the emotion as a painful emotion or a happy emotion. Thought creates feelings. Be aware and pay attention to what you are thinking, believing and feeling. Consequently, you will not make a mess of your feelings. Stimulus + Thought = Subsequent feeling.