lǚ shì bù shuǎng
◎每次使用都有效；多次试验都不错。
例如这种新农药效果良好，屡试不爽。
英文be found officious as often as it is tried; be often tried and often succeeded; effective every time it is used;
◎屡次试验，结果都相同。
例如如：“这个方法十分有效，屡试不爽。”