It's a very important question: why do we build? While we can come up with a myriad of answers, such as to have a home, or a place to gather, raising the inventory of our property, etc., it still misses the essence to some extent. We build, I think, primarily out of a physical consideration. Bluntly put, main reason for building = shelter. Architecture is necessary because of our physicality, which acts in an environment where it can be threatened by many dangers, and discomforts, from bad weather to wild animals to other humans, therefore we need to create an environment where it is possible to avoid as much as we can the ruining of our own bodies. In this sense architecture is a tool is aimed, or should be, to fulfil the condition of protecting, and somehow caressing, the users. It doesn't take much. However, if that basic condition is not fulfilled in a building, as in the built object does not allow for any level of liveability, as crude as it may be (like a primitive shed), then it cannot be called architecture.
Without its users, architecture is meaningless. This is probably the first thought that should enter a designer's head when drawing the plans for any building. Considerations such as art, economics, style, etc are ultimately less important than the way the users, and their needs, are addressed. From this perspective, ego is the most incompatible characteristic of an architect; their responsibility is to think about the people who will inhabit that building. If someone cannot think further than his ego, cannot have a basic compassion for his fellow humans, and does not care if their building, or part of it, affects the users in a negative matter, but apologises with considerations such as originality, personal style, etc then maybe they should not be professing architecture.