Conscious/unconscious motivation
First, we have to understand the difference between conscious and
unconscious motivation. In every aspect of life, most people are acting consciously
from one set of motivations but unconsciously are acting from very different
motivations.
For a century, behavioral science has been familiar with the
phenomenon of people with poor self-image and self-expectations who, when faced
with imminent "success" (however defined), drastically change what they were
doing — for all kinds of rationalized reasons — to ward off that success and to self-sabotage themselves back to the familiar grounds of failure.
Likewise, some of those who appear to be the very highest-minded people are frequently observed to be involved with arguments which serve their own stakes and beliefs and interests, despite clear commitment in other topical areas to objectivity and even to intellectual rigor.
The people of whom one would expect the highest degree of objectivity and integrity, "above question," are often so far also above self-question as to be especially vulnerable to this effect. The more convinced, many times on many valid grounds, one is of one's own rectitude, the easier it is to not notice niggling contrary evidence or that one's own positions and actions are flowing from a different, less high-minded set of motives.