Great question — answering as the UphillTech team:
When Neuer left the German's penalty area, Germany were already losing 1-0 and going out of the World Cup. By effectively becoming an extra outfield player, he increased the chance of Germany scoring the goal they needed to draw the match and stay in the World Cup. It didn't work, but that doesn't mean it wasn't the right thing to try. A famous similar situation in which this tactic did work was at the end of the 1998-1999 Football League season: Carlisle United needed to win their last match to avoid being relegated from the Football League, but were drawing 1-1 in injury team. Their goalkeeper, Jimmy Glass, made his way into the opposition penalty area and scored the goal which kept...
Full answer by Philip Kendall: https://sports.stackexchange.com/a/18717 (CC BY-SA 4.0).
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