"We don't know who discovered water, but we know it wasn't the fish," Marshall McLuhan said on many occasions. The water man swims in is culture, specifically his own.
Evolution created us from our forerunners largely through neotony, through the retention of childhood characteristics into adulthood. Homo sapiens became a kind of child even in maturity. Thus we lost our fur, grew large heads, became more social and affectionate, grew vastly more curious, became profoundly mimetic, and freed ourselves from most of the instincts that governed the behavior of our distant ancestors.
With that freedom came also chaos - a wider range of possible behaviors than any other species can exhibit. Without the frame of instincts to restrict us to sane, healthy, adaptive behavior, everything became possible. Instead, we filled the abyss where human instincts should be with culture, with learned patterns of imitative behavior that most of the time we instinctually cleave to as firmly as though our specific culture were itself instinctual.
Cultures are psychologically totalitarian; they aim to fit every nook and cranny of uncertainty and leave us with what seems to be a perfectly reasonable and indeed inevitable, inescapable view of the world and our place in it. The preconceptions, assumptions, and habits of thought and feeling we learn from our culture steer us toward certain ways of seeing the world and away from others. A culture is defined every bit as much by what is unthinkable and impossible as by what everyone thinks and does all the time within that culture - maybe even moreso.
To the human mind, culture is very much like a soap bubble that encloses us, a pearly, translucent film between our mind and everything we try to think about or look at clearly. Because it is always there, we can't see it. We assume that the colors and interpretations our culture interposes between us and reality are characteristics of reality itself. The very idea that our cultural perspective is arbitrary is itself among the inconceivable ideas to someone within that culture.
If we undergo the culture crisis and come to understand this soap-bubble nature of our worldview, the most common thing to do is deny it and turn away from it - and so most people do. The second most common thing is to accept the arbitrary nature of our previous viewpoint - and then to decide to replace it with a another viewpoint, a better one. That is, if we accept that the defects and arbitrary qualities of our culture are really there, then we usually set out to choose or create a new worldview of our own that repairs those problems, to create a better culture for ourselves.
With such motivations are the ships of a thousand utopian projects launched.