I agree, detachment is extremely challenging. Even more than detachment from worldly objects, we need to remain detached from our body, our ego, and our thoughts and feelings. They are ours, yes, but we don’t need to be attached to them. The real us is separate from all of those things, so by striving for detachment, we can get closer to that.
I don’t think it’s an unattainable quest. I don’t think it has anything to do with us being mortals (the human version of Buddha was a mortal too; many people see Buddha as not a person or a god but something much deeper… similar to a philosophy or state of mind).