When something is ‘done in one’, it means that it has been successfully completed or achieved in a single attempt or effort. This phrase is often used to describe a task or goal that has been accomplished without the need for any additional attempts or revisions. It can also refer to a person who is able to accomplish something efficiently and effectively on their first try. In essence, ‘done in one’ implies a sense of efficiency, skill, and success in completing a task or achieving a goal.