Thor's arm loss in the comics can occur due to multiple reasons. Sometimes it's the result of a magical curse or a confrontation with an extremely powerful villain. The details change across different comic arcs.
Rick lost his arm when he faced a challenging situation. The circumstances were overwhelming, and despite his best efforts, he couldn't avoid the injury.
There's a visual novel called 'Fate's Twist' where a guy loses his arm due to a magical curse. The curse was cast by an evil sorcerer and has a significant impact on the character's journey and development throughout the story.