It is a well known phenomenon that the same amateur who can conduct the middle game quite creditably, is usually perfectly helpless in the end game. One of the principal requisites of good chess is the ability to treat both the middle and end game equally well.
Aron NimzowitschIf in a battle, I seize a bit of debatable land with a handful of soldiers, without having done anything to prevent an enemy bombardment of the position, would it ever occur to me to speak of a conquest of the terrain in question? Obviously not. Then why should I do so in chess?
Aron NimzowitschHow is it to be explained that something inside me revolts against the playing of obvious moves? Perhaps we may perceive the underlying reason in the fact that I derive satisfaction from seeking to reveal the concealed meaning of a position by means of maneuvering play and therefore I do not wish to see this satisfaction curtailed by a banal, more or less fortuitous decision. Naturally, this phenomenon is played out beneath the threshold of consciousness. The waking consciousness will, of course, in each individual case, give preference to the more rapid means of deciding the game.
Aron Nimzowitsch