De La Villa on the Endgame
This is very likely the best quote regarding the endgame I've ever read. It explains perfectly why studying the endgame is such a surefire way to improve your rating.
(Entire essay can be found in the introduction to Jesus De La Villa's "100 Endgames You Must Know")
"... I will not say that good command of the endgame is essential, but it is certainly very useful. On the other hand, if you neglect this part of the game, many half points, or even full points, will now and then elude you. And you will rarely get wins in the opening to make up for those lost (half-)points, as nowadays everyone comes to their games armed to the theeth with opening preparation. To put it simply: a player who reaches a certain level as regards theory, strategy and tactics, will lose many points if his mastery of the endgame does not correspond with that same level. Thus, the study of the endgame will be the most straightforward way to improve his rating."