From Mark Weeks,
Your Guide to Chess.
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One of the first world class players to question 19th century opening theory was Richard Réti.

At first it might appear that the Queen's Pawn Opening (1.d4 d5) is nothing but the reflected likeness of the King's Pawn Opening (1.e4 e5). On second thought however, it is really seen that that the Queen's Pawn Opening creates essentially different conditions in regard to the opening fight in the center. - Masters of the Chess Board

What did Réti mean by 'different conditions'? The initial position of a chess game is nearly symmetric. The White and Black armies mirror each other across an imaginary line drawn between the 4th and 5th ranks. In each army, the position of the Rooks, Knights, and Bishops mirror each other across another imaginary line between the d- and e-files.

Only the position of the King and Queen break the symmetry, and this makes all the difference between 1.d4 and 1.e4. As discussed in the parallel tutorial Introduction to 1.e4, the battle after 1.e4 revolves around White's desire to play an early d4. Because the d-Pawn is automatically protected from behind by the Queen, Black can't prevent White from playing an early d4.

After 1.d4, Black has several moves, like 1...d5, which stop White from playing e4 during the early moves of the game. The only way White can force e4 is by granting a concession elsewhere. For example, 2.f3 prepares 3.e4, but weakens the squares around the King and takes away the best square from the White King's Knight.