underdo

It is distinctly unhealthful either to overdo or to underdo work, play, rest, or sleep.
How to Live|Irving Fisher and Eugene Fisk
A young fellow should be ambitious to shine in everything—and, of the two, always rather overdo than underdo.
The PG Edition of Chesterfield's Letters to His Son|The Earl of Chesterfield
A young fellow should be ambitious to shine in everything; and, of the two, rather overdo than underdo.
A Letter Book|George Saintsbury
The English overdo or underdo everything, and are either drunk or in despair.
Winterslow|William Hazlitt

With all their attention, however, they sometimes overdo the business, and sometimes underdo it.
An Inquiry into the Nature and Causes of the Wealth of Nations|Adam Smith