I think that it's Uncertainty.We are also attached to the first instinct which is Survival. This raises the question as to why we are so interested in Survival. One can say it is because we fear Death, which in itself would create a vicious cycle, e.g. why do we fear Death?
We are generally attached to the world which is all we know, and we wish to live forever. We are attached to friends, family, camaraderie ....many things, but the root cause is Desire.
However, I am returning to uncertainly. Indeed we feel fear and uncertainty all our lives. What's going to happen if I walk down that dark alley or catch the midnight train home, or Jack walks out leaving me with the two children?
Will she marry me or find someone else? What would happen if Joy gets offered my job? Will I get another or be able to cope financially? Why do I look right and left when I cross the road? I fear death, so again I ask, why?
From a profound spiritual standpoint, the nature of the Soul is to seek Freedom. We are living in isolation from our True Source, and the Soul knows this either consciously or unconsciously. Why do we fear pain? Because we wish to be free of pain. (immortal), The mind and emotions wrongly identify with this Freedom, as that which it obtains here, and as such fears all that would appear to take it away. The Soul knows, but is still a sojourner in harmony with God's plan.
There is a cloud of unknowing hanging over death and it is very difficult for most mortals to face. Funny my penultimate poem was on death, I believe. I have three positive poems on this subject, and there are many on the Net by Rumi and one by ... (forgot). It is called Do Not Stand at my Grave and Weep. Caroline Norton or Mary Elizabeth Fry. Check it out. Much Love this Sat bank Holiday, Grace. Peace.