Chess Opening Theory/1. e4/1...c5/2. c3/2...Nf6/3. e5/3...Ng8

3...Ng8?
This retreat is just too cowardly and timid. Black has lost two tempi moving the knight to g8 from f6. After d4, White has a huge center and initiative. 3...Nd5 is much better, since the knight is well placed there. It is usually unwise to move a piece back to it's original square in the opening.