It's been a while since I've played OTB chess, but I've gotten back into playing it online. Before my break (I was rated ~1400 USCF), I was a heavy advocate of the English Opening:
rnbqkbnr/pppppppp/8/8/2P5/8/PP1PPPPP/RNBQKBNR w kqKQ c3 0 1 [Event "Local Tournament"] [Site "?"] [Date "????.??.??"] [Round "Opponent"] [White "BaroclinicPlusPlus"] [Black "?"] [Result "*"] 1. c4
with the idea that instead of seeing any opening prep that I make not being thrown out the window, I could force my opponent into lines that I felt comfortable playing. For example, if I was preparing the Scotch Game, and was faced with an opponent who played the Sicilian
rnbqkbnr/pp1ppppp/8/2p5/4P3/8/PPPP1PPP/RNBQKBNR w KQkq c6 0 2 [Event "?"] [Site "?"] [Date "????.??.??"] [Round "?"] [White "BaroclinicPlusPlus"] [Black "Well Prepared Opponent"] [Result "*"] 1. e4 c5 *
I'd be in murky waters. So to prepare for the Scotch Game, I'd have to learn the Sicilian Defense, Caro-Kann defense, French Defense, and any other defense I could see.
My question is this: If you do not know your opponent ahead of time, what advantage is there in preparing openings like 1. e4 when your opponent can nullify any preparation?
That is, most opening prep for white relies on Black playing 1. ... e5, which is not only avoidable, but also lines that I am not usually prepared. The same can be said about 1. d4 and the Queen's gambit (ignoring the increasing popularity of the London System). I've tried moving beyond the English, just to be left with either needing to learn a ton of theory and opening traps or face a better-prepared opponent.
*Speaking from experience, where I have a Black defense for 1. e4, 1. d4, and 1. c4.