There are as many ways to be adorable as there are dogs in the world, but for my money, the dogs with one ear up and one ear down are the crème de la crème of cuteness. There is something so charming—and disarming—about a dog who is asymmetrical in this way, especially if it is combined with a head cock to further the effect. The ears-askew look can make even the roughest, toughest, most intimidating-looking dog appear totally harmless, and for dogs who already appear to pose no threat, it makes them even more lovable.
So, why do so many dogs have one ear up and one ear down? In some cases, it is a young dog whose ears are part of the way through the process of growing into an erect posture. They have not done it evenly so one ear is further along than the other. The cartilage in the ears is soft, but usually grows strong enough to support the ear as the puppy develops. Some dogs permanently remain in the one-ear-up, one-ear-down phase of life.
via Whisker Therapy