A doubt for other person is like a black colored goggle on our eyes, which shows every action of other person as black to us and we ourselves are not aware that the goggle is ON.
It happens that we assume something about some other person and then we start seeing every action of other person in accordance with our assumption. Suppose I assume that “You are selfish”, then every action of yours start looking me filled with selfishness. If you come and give me a smile I find that smile sarcastic or plastic. If you come and ask me “How are you?” then I feel that you are making fun of me. If you come to my house, I feel that you must have come to ask for a favor. Every action of yours, whatever you do, whatever you think, however you behave start looking to me in alignment to my assumption. In fact if I have a doubt for you in my mind then I start doubting you in all my previous interactions. I also start finding every action of yours in alignment of my doubt. This situation becomes similar to seeing that particular person through a black colored goggle and finding his every action black.
This doubt is like a “seed” within me. With time and more and more interaction with you this seed start getting sprouted and then start becoming a small plant, then bigger plant and this continues. The more I interact with you with this seed alive within me the more I nurture it within me. If I keep this seed alive within me for a long time and this seed grows to a bigger tree then it starts hurting me terribly inside. I become very uncertain about the person for whom I have this seed of doubt and my behavior with that person start changing. Now, if this seed had come into me without other person really having any problem then due to change in my behavior with other person, other person starts getting a doubt. If we both do not communicate then after some time we find that we both are not even talking or the strength of relationship is reduced a lot and in reality there was not really a problem in the beginning!
A person who used to look me like this before doubt,
After I have got a doubt for that person then he starts looking me like this,
Beauty of the person start converting into Beastliness. This whole problem started with the “seed” of doubt which developed within me.
This problem is of Relationships. The root cause of all this problems lies in, Lack of Trust and Respect in Relationships. We lack assurance in relationships to ask other person if there is something wrong and in most of the cases we are very much afraid that what impression it will give to the other person and ultimately we end up loosing the relationships. Relationships are generally not in our priority. We are generally more afraid about our impression on other person and end up loosing impression and relationship both.
In reality Feeling of Relationship is something which is a basic need of a human being. A human being wants to live with Trust and Respect within himself and also in Relationships. This willingness to live with Trust and Respect is something which is continuous and is ever actively present. A human being expects Unconditional Acceptance from other person but lacks the competence to give it to others. Where a human being feel that he is getting Unconditionally Accepted he start bending towards that direction and the moments he feels that now he is no longer getting accepted from the people or he gets fear of getting nonacceptance then he starts running away from them.
In most of the cases the thing which is happening is, everybody wants to get accepted from others around him but lacks the capability to accept others around him. This gives rise to a situation like two beggers are trying to snatch coins from each others bowls. It gives rise to deprivation, exploitation, opposition, coruption, wars and world wars. It is a chain and unfortunately we all are into it.
To understand Human, Human Relationships, Trust, Respect, Unconditional Acceptance etc. we need Knowledge.
Knowledge includes understanding related to:-
Self
Family
Society
Nature.

Very good. I like that, especially the ending paragraphs
“This problem is of Relat…” and “In reality Feeling of Relat…”