Verb
become ground down or deteriorate
Source: WordNetDo what you love. Know your own bone; gnaw at it, bury it, unearth it, and gnaw it still. Henry David Thoreau
Afterwards I learned, that the best way to manage some kinds of painful thoughts, is to dare them to do their worst; to let them lie and gnaw at your heart till they are tired; and you find you still have a residue of life they cannot kill. George MacDonald
I had nixed the idea of having children when I was myself a child, having learned in the 1960s that human overpopulation was literally crowding other species off the planet. Why create another mouth to gnaw at the overburdened earth? Sy Montgomery
Her confidence eroded Source: Internet