We can conceive of nothing more fair than something which we have experienced.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“Are they prepared for a better than they can now imagine? Where is the heaven of him who dies on a stage, in a theatre? Here or nowhere is our heaven. “Although we see celestial bodies move Above the earth, the earth we till and love.” We can conceive of nothing more fair than something which we have experienced. “The remembrance of youth is a sigh.” We linger in manhood to tell the dreams of our childhood, and they are half forgotten ere we have learned the language. We have need to be earth-born as well as heaven-born, γηγενεὶς, as was said of the Titans of old, or in a better sense than they.” source