one of the episodes jiraiya says something about how the nine-tails chakra is released whenever naruto is in danger. this is true because he threw naruto down the waterfall because jiraiya new that the nine-tails would lend naruto its chakra to save naruto, because if naruto dies the nine-tails dies as well. maybe naruto's dad knew naruto would benefit from the nine-tails by obtaining its chakra, the 4th did create that technique :/