Keep on Training: Pop Goes the Water Balloon!

is episode 87 of the original Naruto anime.

Synopsis
Soon after his training begins, Naruto finds himself unable to make any progress. After asking Jiraiya for tips, Naruto decides he'll master the jutsu in three days. Jiraiya doubts the likelihood that Naruto will live up this promise, explaining that the technique's creator, the Fourth Hokage, took three years to develop the Rasengan in its current form. He then goes on to explain that popping the balloon is only one of three steps to mastering the tehcnique, and leaves Naruto to resume his training.