The bittern, a bird found in swampy areas, has inspired a wide range of literary works, ranging from realistic portrayals to symbolic interpretations. Henry David Thoreau references it in Walden as an emblem of wild, unspoiled nature, while Adam Clarke and others use "bitterness" as a metaphor for human anguish and ethical struggles.
Writers like Louis Couperus and Warwick Deeping explore emotional distress, portraying bitterness as an obstacle to comprehension, whereas John Wesley highlights its harmful influence on society. This dual nature—both literal and symbolic—demonstrates the theme's ability to connect environmental observation with psychological insight.