no rhyme or reason
From Longman Dictionary of Contemporary Englishno rhyme or reasonno rhyme or reasonREASON#no sensible reason or organization There seems to be no rhyme or reason for the school’s behaviour. → rhymeExamples from the Corpusno rhyme or reason• There seemed to be no rhyme or reason to the colors.• It claims that there is no rhyme or reason to stock-market investment.