Lesson
White to move. Main line: 1. c4 c5 2. Nc3 Nc6 3. g3 g6 4. Bg2 Bg7 5. Nf3 Nf6 6. O-O O-O
The mirrored development controls d5 from both sides and keeps the central pawns flexible. Each bishop pressures the long diagonal, while the knights and kings reach natural squares without creating an immediate weakness.
Symmetry is temporary because White moves first. White can use that tempo for d4, b3 and Bb2, or a queenside expansion; Black often seeks ...d5 or waits for White to define the center before choosing a counterbreak.
Do not copy moves mechanically in symmetrical positions. Compare who benefits if the center opens now, which side can occupy d5, and whether a pawn exchange activates the opponent’s bishop. Those questions explain when the apparently equal structure starts to diverge.