In his book A Brief History of Everything, Ken Wilber makes a simple but important point. He says that as things go through the process of evolution, they will inevitably transcend and include their earlier stages of development. In other words, each higher step on the evolutionary ladder not only transcends all the previous steps but also includes them.
An obvious example is the multicellular organism that both transcends and includes the individual one-celled life forms that gave rise to it. Another example is the molecule that transcends and includes the atoms of which it is constituted, just as the atom transcends and includes its subatomic constituents.
But where the idea is really useful is in the evolution of consciousness. Probably the best book I’ve read on this subject, at least from a scholarly perspective, is Changes of Mind by Jenny Wade. Though Wade’s book is written in rather dry and technical language and is not always easy to read, it comprehensively outlines the stages of development of consciousness all the way from the prenatal to the postmortem (as indicated by near-death experiences). Wade does a fine job of showing how each stage of consciousness transcends the previous one — but I’m not sure she is equally clear in showing that the higher stages also include the lower stages. Yet this insight seems critical to me. It means that, no matter how far we may travel in the development of our own consciousness, we will still embrace what we might call the "lower elements" of our nature. To put it another way, even if we manage to largely transcend ego-based behavior, our ego will still exist, and we will still find ourselves acting egoically in some situations.
And this is not necessarily a bad thing, because there are circumstances in which an egoic reaction is probably the most desirable. We do not, after all, want to become doormats who let people walk all over us.
The ideal outcome is not to lose the ego entirely, which is probably impossible anyway, but to minimize the extent to which the ego controls our behavior. The ego then becomes part of a repertoire of possible responses in any given situation. Most of the time, an ego-based reaction will be counterproductive — but not always.
Maybe there are some spiritual masters who reach such an exalted stage of personal development that they no longer have any ego-based responses at all. But I suspect that this level of development, if it exists, is exceedingly rare. More often, we may see through the illusion of ego-based behavior in most circumstances but still fall back on it occasionally. Even Jesus is depicted as becoming angry and violent at certain points in the New Testament — when overturning the tables of the money changers, for instance, or in his heated arguments with the Pharisees. This is not to say that a spiritual master like Jesus did not transcend the ego, but only that in transcending it, he still included it as part of his makeup.
Anyway, the idea seems useful to me. It means we don’t need to beat ourselves up on those occasions when we revert to immature or even infantile behavior. The possibility of behaving like a child or spoiled teenager or a narcissistic twentysomething remains part of our nature even if, for the most part, we’ve moved beyond it. We never lose anything. We transcend and include.