... Averbakh's Comprehensive Chess Endings, vol 4, Pawn Endings ...
"I conceived the idea of writing a popular booklet [Chess Endings Essential Knowledge] devoted to the endgame back in the early 1950s, when I was working on an encyclopaedic reference work intended for players of high standard. Out of the mass of information on the endgame, I thought it was important to select the minimum which any chess enthusiast should know in order to handle competently the concluding phase of the game. It turned out that it was not necessary to know such a great deal." - Averbakh
... Mark Dvoretsky explains it well in Dvoretsky's Endgame Manual.
Page 20 of the 4th edition.