Often the weakness of an advanced pawn is not so much its liability to be attacked, but in the loss of control in a neighbouring file. Colin Crouch & Kean Haines, Hastings 1895
4.Bd2 (in the Nimzo-Indian) has been heavily slagged off in the popular press. The criticism runs along the lines of "this move is just too passive." My opinion is that any move which serves a useful purpose (in this case unpinning) must be treated with some respect. John Emms, Easy Guide To The Nimzo-Indian
The Scotch Four Knights is an ideal choice for the improving player, whether playing White or Black. The variations are neither too complex, nor theoretical, both sides develop easily, and the open positions are ideal for honing tactical skills. John Emms, Starting Out: The Scotch Game
Exchange sacrifices on c3 to expose the opponent's king are often very strong in the Sicilian. Do though try to ensure that you have more attacking pieces ready to follow one up than there are defensive pieces of the opponent's. Richard Palliser, Starting Out: Sicilian Najdorf
The same general principles apply to openings and middlegames: the importance of the centre, rapid and efficient piece-development, king safety. Yet in the endgame these factors are only noteworthy by their absence. Edmar Mednis, From The Middlegame Into The Endgame