Naruto Uzumaki: Everyone... everyone... has risked their lives to come after you.
Sasuke Uchiha: Well, how good for them.
Naruto Uzumaki: Believe it.
Kakashi: Uh, Naruto, your speech was cool and all, but if you lose any more blood, you're going to die.
Deidara: Art is... with a bang.
Rock Lee: A dropout will beat a genius through hard work.
Answer: In-character, he's not very good at Bunshin No Jutsu, so it's unreliable. Out-of-character, it's a classic plot device shared by hundreds of anime that people who're not generally too great can do spectacularly well when it really matters.
Moose ★