What's the point of learning opening theory?

A four-board match played away at Exmouth one Saturday:

The top board players each made a mistake on move 5: 1.c4 e5 2.g3 Nc6 3.Bg2 f5 4.Nc3 Nf6 now 5.e3(?) was possibly inaccurate, allowing 5...d5! (see Kosten’s book) but Black didn't play it, preferring 5...Be7.

Board 2, they both scampered along a main line of the French Tarrasch: 1.e4 e6 2.d4 d5 3.Nd2 Nf6 4.e5 Nfd7 5.Bd3 c5 6.c3 Nc6 7.Ne2 cxd4 8.cxd4 Qb6 9.Nf3 f6 10.exf6 Nxf6 11.0-0 Bd6 This is the tabiya, where the real first choice lies for White: 12.Nc3 0-0 13.Be3 Bd7 14.Re1 Be8. Now here all the books give this position as equal; although it is unbalanced I don't know why White wants to play this line. We than had 15.Ng5 (a very important move) and then 15...Bh5? which was the first deviation from theory... White can now get an instant plus with 16.Bxh7+! e.g. 16...Nxh7 17.Qxh5 Nxg5 18.Qxg5 Nxd4? 19.Nxd5! but it was not refuted by White's chosen move, 16.Qb1?! ...

Board three was a bit less theoretical, although it has been played before: 1.Nf3 g6 2.e4 c5 3.Bc4 Bg7 4.0-0 e6 5.c3 Ne7 6.d4 cxd4 7.cxd4 d5 8.exd5 after which Black surely should not have played 8...exd5(?) but 8...Nxd5, when there is some sort of plan against the IQP instead of a 'normal' White small plus with no prospects for Black.

And Board 4 had the unlikely start 1.e4 c5 2.Nf3 d6 3.h3...

So, opening preparation can be a complete waste of time!

"For example, I spent a couple of years studying all the possible transpositions in the Noteboom, but then guess what? Almost nobody gave me a chance to play it, preferring an early e2-e3 and the Anti-Meran..." Ruslan SCHERBAKOV