Until you train in your gear, you don’t know how tough an operation can be.
You may be really fit… doing your squats, deadlifts, and everything else in the gym. But when you put your gear on, you have dynamics of restriction.
You have additional weight that you’re not used to dealing with.
But it’s not a weight that you’re lifting anymore.
Now it’s a weight that you’re wearing on your body.
Maybe you have a backpack on and it’s really loose, and it’s swaying back-and-forth as you’re trying to run. Not only do you have to perform the task of running to your objective, but you also have to deal with the forces pulling you side-to-side as you run forward.
The last thing that you want when you’re squatting, running, and jumping, is a bunch of weight shifting around.
Because that’s additional momentum.
When you have additional momentum, you’re wasting energy trying to counterbalance your gear. This makes any task more difficult.
So anytime you can stabilize the load closer and tighter to your body, the task will be easier.