On the field trip, my backpack was a stubborn mule, dragging me backward as the trail tilted up the hill. With each step, the straps bit into my shoulders like small teeth, and my breath puffed out in short bursts. I wasn't carrying anything alive - just lunch, a water bottle, and my sketchbook - but it felt as if the pack had its own grumpy mind, refusing to move the way I wanted. I leaned forward and tightened the straps, hoping to coax that mule to cooperate, but the weight still tugged at me, making the climb slow.