The wrath of God lies sleeping. It was hid a million years before men were and only men have power to wake it. Hell ain’t half full.
Beneficial magic items often come about through intentional enchantment. Typically an enchantress will decide what sort of magical effects she desires to imbue upon an object, gather the requisite eldritch knowledge and mundane materials, and will either craft the object or saturate a pre-fabricated object with the appropriate boons. These enchanted items are nigh-always beneficial to their users, as befitting the expenditure of time, expertise, and materials required for their creation.
Very occasionally the item will be hexed, designed to cause some deleterious effect on the bearer. These are manufactured, if ever, for the injury of some remote, inaccessible, or well-protected target—the expense of common use quickly becomes prohibitive. There are far cheaper, easier ways of wishing someone ill.
Cursed items, properly, are truly cursed, rather than intentionally hexed. Tragedy, blood, and the most malign of intention can impress themselves onto the mundaneness of objects; envy, cowardice, or simple rage will also do. Any sufficiently strong or sufficiently negative emotion can quite unintentionally become imprinted on a material substrate. Such a thing becomes cursed.
As pseudo-hexes unguided by conscious intent, curses tend to replicate in effect the circumstances of their creation. Consider the man who, through derangement or demon-influence, begins thinking that his family are actually impostors, fey-placed fetches sent to torment him. He takes up his hammer and murders them in their beds. This is an act of wickedness that cries out to the gods. That hammer—regardless of the fate of the man—may become cursed. Thenceforth it will, if ever taken up again, exert a malign influence on its bearer. It may become useless for smithing, turning aside when swung in useful work; it may refuse to move in the hand if used in combat against a dangerous foe; but it may leap to grisly work when the holder sees anyone who resembles (to whatever degree of resemblance) the slain family.
No wizard enchanted this hammer. But cursed it is, and woe betide the adventurer who plucks it up as loot.
A cursed item is likely very difficult to be rid of. Let’s think back to the creation of a magic item. An enchanted item—conveying some sort of boon—is easy to transfer. Either it has been enchanted so as to be ambivalent as to its owner, or what power it contains wants to be put to its best and highest use, and ready transferability facilitates that. (An intentionally hexed item, by contrast, is probably hexed so as to be unriddable by its victim.)
But a cursed item knows in some ineffable way that it is unwanted. In the same sense that wildfire knows to spread or winter knows to be cold, the accursed thing knows that any person it touches would otherwise be likely to toss it in a bonfire or throw it down a chasm. It does not want to let go. How this manifests is individual to the object and the circumstances of its creation. The cursed hammer above may simply be impossible to set down, or it may reappear in hand whenever a woman or child is nearby, or it may ensorcel the bearer as to never desire to be rid of it. Another object, like the One Ring, may cause a pathological possessiveness in all who see it. Another may simply shadow a person, like an ioun stone that cannot be grasped or a wraith-pennant forever fluttering from the head of a weapon.
There are ways of being rid of a cursed object. There are even people who make it their lives’ work to expunge the world of them. But that is the topic of another post.