Basic training in the United States Army is no joke. If you know of anyone who thinks the contrary, show them the following video. As far as evidence goes — it’s all you’ll need.
The particular instance captured is actually part of Cadet Basic Training, and shows 2018 Cadet Bradley Gibson powering through his time in the gas chamber without a mask while reciting the Soldier’s Creed and nearly succumbing to the poison he’s inhaling.