Mario Gotze Germany's national player who scored the only goal in the 2014 world cup final in Brazil he is about 22 years old, as far as I remember he was only installed at the beginning of the tournament as a starting XI but then he was always a substitute including the Final.
Gotze is young in that World Cup but he actually made his name in Borrusia Dortmund and already was an important player in Dortmund back in that season. He debuted in Dortmund in 2010 and before that World Cup, Gotze already played more than 150 matches for Dortmund.
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But during the extra time in final, his goal made Germany the champion for the 4th time. It's a very impressive match until now
He was no longer a potential player but actually a star player. Even so he did not get a good position in Germany squad but at the end of World Cup, he helped them to take the trophy.
However, did not have such an impressive record on their debut in the 1998 world cup. but there is one that I can remember, Michael Owen, where he made his debut with the England squad at the world cup in France in 1998 at the age of 18, and managed to become a player the best youth at that time. but unfortunately, he could not give the title of champion for England.
Owen is a similar case like Gotze as he already got a very good position in Liverpool before World Cup 1998. It is not like Ronaldo (Brazil), Baggio or Kaka, they were all too young players and not get good positions in big clubs like Gotze or Owen. In fact, Owen (
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Their national coaches gave them opportunities to join World Cup tournaments because they wanted to give those players chance to learn and grow up. Those coaches knew that they will not use those young players in World Cups.