Definition.com
Earnestness is good; it means business. But fanaticism overdoes, and is consequently reactionary.
Definition.com
Earnestness is having an honest distrust of oneself, to treat oneself as a suspicious character, as a financier treats an unreliable client.
Definition.com
Earnestness is the best gift of mental power, and deficiency of heart is the cause of many men never becoming great.