Insecurity in relationship arises if there is a certain degree of emotional dependency upon the friend or partner. There is a fear of losing the friendship and hence the mind tries to possess the person. This possessiveness leads next to a wish to control which obviously becomes counterproductive.
What one needs to understand is that, first and foremost this world is deeply interconnected and hence an exclusive friendship with one person is a near impossibility unless one lives in a place where there are no means of contact with anyone else. Secondly, an individualized person, especially strong personalities need space to navigate their life and do not like to be controlled by anyone. It is natural that if everything is shared the partner will have his or her views and a natural tendency to advice or comment on the choices one makes. This evidently creates friction because it is very unlikely that two people will think, feel, act in the same way. Even if there are affinities in certain areas, there is likely to be dissonances in other areas, especially if the personality is complex. Therefore sharing everything, idealistic though it sounds, leads often to misunderstandings. It is this subtle truth of human psychology that has inspired the Shakesperean adage ‘too much closeness breeds contempt’ and the sage advice of the Lebanese mystic ‘let there be spaces in your togetherness ‘.
In fact just as two trees growing too close may hamper each other’s growth so too an excessive closeness leads to a stunting of natural growth in another. It is only when two persons have develooed completely, grown to full maturity that they can share everything and laugh together freely without fear of being judged or criticised. That is very rare. Hence it is best not to insist on sharing everything if you want the friendship to remain healthy and last long.