It is sometimes expedient to forget who we are.

We may with advantage forget what we know.

It is sometimes expedient to forget what you know. [Lat., Etiam oblivisci quod scis interdum expedit.]

Do not turn back when you are just at the goal.

Never thrust your own sickle into another's corn.

One ungrateful man does an injury to all who are suffering. [Lat., Ingratus unus miseris omnibus nocet.]