<p>It's like in 3x13 of ATLA, in <i>The Firebending Masters</i>. Zuko wants to teach Aang firebending, but suddenly he can't - what happened? He lost his
source. He always <i>relied</i> on his inner rage and that's where he drew his power from. So when that was gone, he had to search for a new source.
</p><p>The same applies to waterbenders, who learn to push and pull water <i>like the moon</i>, so when it is suddenly gone, it's not only a spiritual shock for them. I mean, we have to block out the fact that the moon can't really be killed. But
I've already covered that at some point. So in the end, it comes down to the fact that firebenders don't rely on dragons to bend, but waterbenders more or less rely on Tui & La, who are connected to the physical ocean & moon.
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