Towards the outside, at any rate, the ego seems to maintain clear and sharp lines of demarcation. There is only one state – admittedly an unusual state, but not one that can be stigmatized as pathological – in which it does not do this. At the height of being in love the boundary between ego and object threatens to melt away. Against all the evidence of his senses, a man who is in love declares that ‘I’ and ‘you’ are one, and is prepared to behave as if it were a fact.
The ego represents what may be called reason and common sense, in contrast to the id, which contains the passions.
It is easy to see that the ego is that part of the id which has been modified by the direct influence of the external world.
Children are completely egoistic; they feel their needs intensely and strive ruthlessly to satisfy them.