the exception that proves the rule

Từ điển Oxford Advanced Learner 8th

the exception that proves the ˈrule idiom
(saying)people say that sth is the exception that proves the rule when they are stating sth that seems to be different from the normal situation, but they mean that the normal situation remains true in general
•Most electronics companies have not done well this year, but ours is the exception that proves the rule.
Main entry: ↑exception_idiom