Complete understanding is reached when a person realizes that their understanding is incomplete, and that there will always be another explanation and another perception of the same concept. The most brilliant attribute of the concept of understanding is that it is never-ending. A great mind is one who realizes that they will never reach complete understanding, but continues to attempt to grasp it and allows others to do the same. I remember sitting in science class with a frown on my face several times. Not being able to understand something is frustrating especially when a GPA is mixed into the equation.
Understanding involves several different emotional and mental processes.
It is difficult to define understanding because these processes occur internally. The individual might, in some cases, be the only true judge of whether he understands something. A person can have a feeling of comprehension that is not explicable to others. However, this feeling is different for everyone and is a vague and fairly useless description of understanding. The neurological process is complex and not fully understood.