the morally upright have a hard time making friends; fish will not live in water that is (too) clean
Proverb meaning that a person who is too strict or pure may find it difficult to get along with others, just as overly clean water cannot sustain fish. Often used to advise flexibility or tolerance.
As the saying goes, 'fish will not live in water that is too clean,' so you should be a bit more easygoing.