We, as a society, have created an agreed upon standard that everyone accepts to be the truth. Each person must realize, accept, and understand this truth through their own eyes, and because no two people are exactly the same, no two understandings can be the same. However, we must learn how to reach understandings just as we must learn to do everything else. This becomes a very egocentric quest in that we begin to assume that our understanding of a piece of information, or of a person or idea is the same as all understandings, and that no other form of understanding exists. This understanding is based upon the assumption that every other person understands as they do, and not that each person reaches their own individual understanding that, in turn, derives the correct answer.
Understanding is as abstract as any other philosophical endeavor.
In order to understand anything completely, you must realize every possible viewpoint that has ever existed. We can learn Darwin's theory of evolution, and feel that we understand it in every way possible, but nobody knows exactly what drove Darwin to his conclusions or exactly why he reached them. In the same light, Darwin could not possibly have understood his own theory from every possible viewpoint, including those that had not even been realized by the time of his death. Although the quest for complete understanding may seem fruitless, it is not in any way unimportant. 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.