I have to call it a sin, rather than an error, because it is a choice made despite our better instincts - nonetheless it is so common, so universal, that it is almost asif the sin is a part of normal socialisation, of growing-up in The West.
The sin is 'materialism' - which could also be called positivism, reductionism, scientism... it is the standard assumed view of all public discourse for several generations, so it doesn't have a commonly used name; since we don't name our assumptions, and are seldom even aware of them.
Materialism is what blocks that which is most necessary for us to be aware of: which is our knowledge of the reality of that 'matrix' of Beings which make up this world. The awareness that this world is alive, conscious and has purpose. We all have this knowledge, but we lack awareness of this knowledge and deny it by assumptions that (at some point in our development) we have chosen to adopt.
It is all One Big Thing, really - but there are various aspects to the assumption:
Deadness - There isn't even a word for this assumption, which almost everybody assumes... It is that ultimately everything is or will be Not Alive, but Dead. We exist in a Dead universe (the stars, planets, moon are all Dead; all submicroscopic stuff is Dead), and living things are made of Dead components. Ultimately, everything is reducible to Physics, and the entities of Physics (waves, particles, forces etc) are Not Alive, not Conscious, lack innate purpose. What is denied is our inborn assumption (and that of most people in history) that reality consists of living, and (in different ways) conscious Beings. Apparently everyone believes this at some level, but Modern man denies it - by assumption.
Entropy - We believe in the reality of entropy - the tendency to chaos, but not of love. Entropy is assumed as a universal reality, an inevitable force, a tendency of everything everywhere - breaking down, corrupting, destroying everything all of the time... but we deny by assumption the reality of any similarly universal tendency in the direction of development, creativity, life, consciousness etc.
Natural Selection - We believe that this is the sole explanation of the adaptiveness and range of life on earth - that it is the origin of life, the only cause of the variety of species, the single reason for the emergence of Man and individual Men. We deny by assumption that any of the above has any purpose; we deny that there is any reason for any of it, we deny any meaning to it. The assumption is that Natural selection Just Is, and Just Does.
You get the idea. Always and everywhere, Modern Man assumes a one-sided view of existence - he assumes that underlying reality is dead, chaotic, going nowhere and without meaning. This has not been discovered but is assumed. This assumption is not natural but chosen; and that choice was personal.
If we call this materialism, then materialism is our great sin.