The phrase "nailing it down" refers to identifying or resolving a problem or issue. Its antonyms could include "missing the mark," "failing to grasp," "unclear," "unsure," "inaccurate," and "vague." When someone is unable to nail something down, their efforts to solve a problem may falter or result in confusion. In contrast, if they successfully nail it down, they are able to make progress towards finding a solution or resolution. By understanding these antonyms, it becomes easier to recognize and articulate when and where "nailing it down" can be improved.