Why is e6 "forced" in this position? Larry Christiansen has played and analysed his four games against Chessmaster. 

At the 8th move, he shows a different possible continuation and says that e6 (shown below) is forced for black. I don't see why black would be any worse if another move is played, so why is this forced? For instance, is g6 not possible?



[FEN ""]
1. Nf3 c5 2. e3 Nc6 3. c4 Nf6 4. d4 d5 5. cxd5 Nxd5 6. e4 Nf6 7. d5 Nxe4 8. dxc6 Qxd1+ 9. Kxd1 Nxf2+ 10. Ke1 Nxh1 11. Bb5 b6 12. c7+ Bd7 13. Ba6 e6
White has some nasty threats involving the loose a8-rook and c7 pawn. After 13...g6:

[FEN ""]
[StartPly "26"]

1. Nf3 c5 2. e3 Nc6 3. c4 Nf6 4. d4 d5 5. cxd5 Nxd5 6. e4 Nf6 7. d5 Nxe4 8. dxc6 Qxd1+ 9. Kxd1 Nxf2+ 10. Ke1 Nxh1 11. Bb5 b6 12. c7+ Bd7 13. Ba6 g6 14. Bb7 Rc8 {Saving material} 15. Bf4 {Defending the passed pawn} Bg7 {Carrying on with the planned fianchetto} 16. Bxc8 Bxc8 17. Nc3 {White will be able to take the trapped h1 knight soon or even play Ra1-d1-d8#}


However, playing 13...e6 allows the black king to attack the c7 pawn, preventing white cramping down like this.



N.B. Not checked by an engine. These are just my first impressions.