As a beginner, one quickly learns about chess principles, and in particular, opening principles.
The first openings most beginners learn are the Open Games. These were historically discovered first due to them being so logical and principled.
From the four objectively best replies to 1. e4, 1. ..e5 seems to be the most logical to me, closely followed by 1. ..c5.
..c6 theoretically and objectively speaking is on par with the aforementioned moves, but seems much less logical to me for the following (not exhaustive list of) reasons:
- c6 takes less space in the center and allows White to grab the full center and a space advantage in the advance variation. In the classical mainline's pawn structure, Black doesn't even have a pawn in the center, with pawns on e6 and c6. Instead of preparing to put a pawn in the center with c6, Black could have placed a pawn in the center immediately with e5.
- to activate the bishop before closing the pawn chain, it needs to be moved several times, and then it is simply traded off by White.
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- ..c6 does not do anything for development. Not only doesn't it open lines for the bishops, it even blocks the natural development square of the knight. c5 seems much more natural for unbalancing the pawn structure, because we achieve c5 in one move, control part of the center from the side, and do not block c6 for the knight.
So what is the reason for it being such a good opening, despite the violation of some fundamental opening principles?
If one assumes that the principles are valid (i.e. breaking them will result in some disadvantage) and that there were no good reasons c6 allows Black to get other advantages in return to compensate the disadvantage(s) resulting from the violation of principles, then there must be a refutation (i.e. White should be able to prove a sizeable advantage).