Chess patterns will often repeat themselves according to the opening that was employed, which is why playing through complete games with a particular opening will help someone play that opening well. Nigel Davies, The Rules Of Winning Chess
Whether you are a new advocate or a seasoned exponent of the English, you will inevitably enhance your understanding by studying complete games, which demonstrate how ideas in the opening are continued into the middlegame and endgame. Nigel Povah, How To Play The English Opening
It's better not to change entire lines or systems, but to tinker a bit so as to make one less predictable, while retaining the knowledge of the ideas behind the lines. Junior Tay, Chess magazine
A growing trend in modern chess is to know as many different openings as possible, making it harder for opponents to prepare. Simon Williams, Chess magazine
Knights and bishops are normally the most important pieces in the middlegame. The reason is simple: rooks and queens are more susceptible to incoming fire than minor pieces. Jacob Aagaard, Excelling At Positional Chess