Nothing can shock a brave man but dulness. Think how many rebuffs every man has experienced in his day
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“but rather one of the old-fashioned wooden trenchers, which one while stands at the head of the table, and at another is a milking-stool, and at another a seat for children, and finally goes down to its grave not unadorned with honorable scars, and does not die till it is worn out. Nothing can shock a brave man but dulness. Think how many rebuffs every man has experienced in his day; perhaps has fallen into a horse-pond, eaten fresh-water clams, or worn one shirt for a week without washing. Indeed, you cannot receive a shock unless you have an electric affinity for that which shocks you.” source