system
Given the following post, respond as if you're commenting on Reddit:
human
[Avatar] Why did the Fire Nation even bother with the drill when Sozin's Comet was only a few months away?

I mean, that drill could not have been cheap. It probably cost them several million gold pieces to build. So why didn't they wait only a few more months for the Comet to come and then just blow the wall away themselves (like Iroh did in the finale) without the need of a giant, expensive drill.
gpt
The Fire Nation shifted its strategy in the 100 years war after the Avatar was found. They moved from attrition and slow conquest to a series of bold and slightly desperate moves to win the war before the Avatar was able to intervene, in case they were not able to capture or kill him. Why did they invade the Northern Water Tribe right when the Avatar sought sanctuary there? They wanted to deny Aang the waterbending training he needed, and hopefully capture him. They could've waited until Sozins Comet to invade and conquer them, but it was better to attempt it then given the possibility of defeat if the Avatar was able to reach full strength. The same with Ba Sing Se.

Necessity aside, war is costly. Time is money and lives. Less war, less death, less cost. Same rationale behind Fire Lord 's plan to burn the Earth Kingdom after the war was pretty much won. Avoid a lengthy and costly occupation by simply killing everyone and starting over.

Anything that would bring the war to an end sooner would be extremely desirable, especially with the threat of the Avatar possibly costing them victory after 100 years of war.