You don't get it. You pull on your boots, and Fido wags his tail; you take out his pack, and he slinks away. That's because he wants nothing to do with that ill-fitting straitjacket you've been strapping on him. Use these guidelines to find him the perfect pack, then help him get used to carrying the weight.
Buy the right pack Pick a size that allows your dog freedom of movement; it shouldn't restrict his legs or his ability to lie down, even when it's fully loaded (i.e. the pack shouldn't fall below his belly). A padded harness and stable packbags also aid comfort.
Adjust the fit Straps should be snug enough to prevent shifting, but loose enough to put a finger underneath. Check straps when your dog is walking and sitting.
Start Small To get your dog used to wearing a pack, begin with short walks with an empty pack. Gradually transition to longer hikes with partilly filled panniers, Only saddle an adult dog with a full load.