To begin from the basics: at first, the infant psyche is totally unconscious. It has no awareness of itself. The ego archetype - the subjective, conscious, human mind - is completely undifferentiated from the Self archetype.
As the child grows, their growing awareness of themselves as a separate being from other people, and especially the mother figure, signifies the separation of the ego from the Self. It is the birth of consciousness, the birth of difference. The ego can no longer continue in its comfortable non-existence within the Self. It is now separated and such separation is experienced as suffering. This is the 'First Impact'. This can also be related to the myth in Genesis in which Adam and Eve are forever expelled from Eden after eating the fruit of Knowledge. Humankind is expelled from Paradise, and must now bear the cross of consciousness, and the suffering that it entails.
In early childhood, the Self archetype is usually projected onto the mother figure. This means that the mother comes to represent in physical reality this experience of totality, plenitude and being taken care of. In other words, she becomes a physical representation of a symbolic archetype. Thus, the child's relationship to its mother figure becomes the blueprint, if you will, to the child's ego relationship to the Self. If there are any problems with this relationship, the child will experience problems with the development of their consciousness, either remaining in an inflated state of hubris (an identification with the Self), or the opposite; a feeling of complete rejection of the Self, resulting in the experience of alienation from the world, a loss of Self-esteem. Clearly, we can see a pattern of rejection in the characters of Eva.
In later life, problems with the ego-Self relationship come to colour all aspects of life for a problem with the Self always indicates a problem with meaning in life; it is a deeply spiritual problem. It is often experienced as a separation from God, and can be expressed in a very negative religious/Mother complex where God/Mother is viewed as dark and threatening. We can see this in the antagonism between the humans and the angels. (If you want to be Freudian about it, you could interpret this as a disruption in the normal stages of psychosexual development; Hideaki probably identifies the problem in the oral stage.) This problem often results in depression and withdrawl, as evident in the pilots, especially in Asuka's fear of double suicide which is triggered by her menstrual cycle (indicating she too, can become a mother).
Thus, this problem in Eva is played out through the various characters; all
of which on a personal and collective (Nerv, Human Completion Project) level
strive towards attaining the 'lost object' of the Mother, or to reconstitute
the damaged relationship between ego and Self. More on the roles the Evas play
in the resolution here.