In the standard line (1 c4 Nf6 2 Nc3 e6 3 e4 c5 4 e5 Ng8) black retreats his knight, thus occupying two of the first four moves with a maneuver that offers literally no development.
this seems very unusual and I'm struggling to figure out the compensation. has white overextended and weakened his position in order to get a development advantage? I'm not quite seeing it