Curses are special form a magic that can only be cased by Warlocks, using gifts bestowed by a patreon. A curse is a powerful form of dark magic created for the sole purpose of manifesting a negative or undesirable effect to a creature or place.
One cannot speak of curses without speaking of its antithesis, the spell Remove Curse.
The curser can always decide to drop the Curse as a Reaction. This is not restricted to Line of Sight, or up to discretion of the GM.
A Curse can always be removed, unless otherwise specified, by a Remove Curse of equal or higher level that the Spirit used to cast it. Sometimes Curses require special steps to be removed, and this is up to the discression of the GM.