Half the variations which are calculated in a tournament game turn out to be completely superfluous. Unfortunately, no one knows in advance which half.
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[Event "rated untimed match"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "Unknown"]
[Black "Unknown545"]
[Result "0-1"]
[Annotator "David Hayes"]
[BlackElo "0"]
[FEN "8/1p6/p3k3/2ppP1p1/3P2P1/1P2K3/P7/8 b - - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
1... cxd4+ ( { Black can try: } 1... c4 2. bxc4 dxc4 3. Ke4 b5 4. d5+ Kd7 5. Kd4 a5 6. e6+ Ke7 7. a4 b4 8. Kxc4 Kd6 9. Kd4 Ke7 10. Ke5 b3 11. d6+ Ke8 12. Kf6 b2 13. d7+ Kd8 14. Kf7 b1=Q 15. e7+ Kxd7 16. e8=Q+ Kd6 17. Qd8+ Kc6 18. Qxa5 Qh7+ 19. Kf6 Qh6+ 20. Kf5 { White wins with a large material advantage. } ) 2. Kxd4 a5 3. a3 b5 4. b4 a4 5. Kd3 Kxe5 6. Ke3 d4+ 7. Kd3 Kd5 8. Kd2 Kc4 9. Kc2 d3+ 10. Kd2 Kd4 11. Kd1 Kc3 12. Kc1 Kb3 13. Kd2 Kxa3 14. Kxd3 Kxb4 15. Kc2 a3 16. Kb1 Kc3 17. Ka2 b4 18. Kb1 b3 19. Kc1 a2 20. Kd1 a1=Q+ { Black wins
with a large material advantage. } 0-1