The Sicilian Defense — 1. e4 c5 — has evolved as Black’s most common answer to 1. e4. First explored by the Italian theorists Greco and Polerio at the end of 16th century, it came to prominence 400 years later with Tal, Fischer, and Kasparov.
With 1…c5, Black creates an immediate spatial imbalance on the wings. If White goes along with Black’s wish for an ‘open Sicilian’ by 2. Nf3 plus 3. d4 cxd4 4. Nxd4, he gains a spatial advantage on the ranks. And because 1…c5 served to free only the black queen, White was ahead in development — that lead increased with 4. Nxd4, centralizing with a recapture.
3. d4 is a sacrifice of sorts. Whereas the old-fashioned gambits gave up material in exchange for time and space. 3. d4 against the Sicilian trades a more vital center pawn for a wing pawn in exchange for time and space.
Advantages in time and space don’t last, so the middlegames find White striving to convert those advantages in time and space into an attack, often at the cost of an imbalance in force.
Black must weather the storm, usually while trying to generate counterplay along the half-open c-file, plus a spatial expansion …a7-a6 and …b7-b5.
The later it gets, the more Black’s additional center pawn grows in importance. In the early-going, Black keeps an eye open for …d6-d5, which usually ensures at least equality (if achieved without pain). As the game goes on, and White’s initiative wanes, Black’s chances to equalize (or more) in the center increase. Also, since White typically makes additional concession to fuel his initiative, those add up in Black’s favor as well.
In brief, White wins the short Sicilian games, while Black wins the longer ones.