Despite careful planning, parts of the event didn't come off as expected.

come 是动词，基本意思是"来、到达"，在这里与 off 组成短语。 off 是副词，基本意思是"离开、脱离"，常与动词搭配表示动作的完成或结果。 come off 这个短语动词的意思是"成功实现、达到预期效果"，常用于描述计划或活动的执行结果。