Proverbs 17:20

He that hath a froward heart findeth no good: and he that hath a perverse tongue falleth into mischief.

A corrupt, wayward and froward heart finds no good. A perverse tongue falls into trouble and mischief. Knowledge and mental cultivation without a corrected heart put powerful abilities in the service of evil. Habitually looking for the faults of others, criticizing them, and holding cynical and unkind thoughts makes it harder to see and appreciate what is good and true. Seeking the good in others and responding with love, praise, and encouragement helps bring out their better qualities.