Physical Conditioning is especially important in hockey, which is a sport that requires complex motor skills in an environment of explosive speed and intense physical contact. Skating, itself, is an unnatural movement for the human body. Add carrying a stick to controlling a puck, reacting to a constantly changing environment, delivering and receiving body checks, going full force for 30 seconds, continually stoping and starting and changing directions...

That's a game of hockey for you.

What does it take to reach top level in any sport?

A tough mental attitude and skill, of course. But without physical conditioning any athlete's capabilities are limited.
Your talent and desire absolutely MUST be supported by a complete conditioning program. That is the only way that players can reach the highest level of performance over the course of a season.
The bottom line is SIMPLE - if you do not work hard at conditioning, you never reach your true potential. In order to become a great player you need a combination of talent and the dedication to work hard to develope it.