Forget the fatigue, focus on your form.
One of my clients and I often have deep talks after we train. Well yesterday I trained him. Ha Ha Haaaa. More like smoked him! Well that's what they call it at Go Ruck. So when the Cadre (Ex-Special Forces who lead the event) are smoking you, they are putting you through a brutal workout. Usually all relatively simple movements which after done for a while, totally suck.
With good habits we can shape our character reliable, dedicated, positive, and empowering to others. On the other hand, bad form can lead us into mental injury, physical laziness, and spiritual starvation.