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.
The way Oliver Queen loses his arm in comics isn't always the same. Sometimes it's a result of a risky mission gone wrong, or it could be from a confrontation with a villain with unique abilities. It all depends on the particular comic storyline.
The reason Wu Zhu lost his memory was because the Temple had erased his memories. In the novel " Celebrating Years," Wu Zhu was a robot. After his memories were wiped away by the Temple, he was even assigned the task of assassinating Fan Xian. Although Wu Zhu had forgotten Fan Xian, out of instinct, he ultimately did not execute the order to kill Fan Xian. After interacting with Ye Qingmei and Fan Xian, Wu Zhu gradually formed his own thoughts and feelings. Although he had lost his memories, he still protected Fan Xian and, in the end, killed the Qing Emperor with Fan Xian. In short, Wu Zhu lost his memory because the Temple had erased his memories.