In "a defence of poetry,” shelley suggests that thoughts and feelings in life are "always arising unforeseen and departing unbidden.” which lines from "mutability” also reflect the idea that life is fleeting?
-we are as clouds that veil the midnight moon;
how restlessly they speed, and gleam, and quiver
-or like forgotten lyres, whose dissonant strings
give various response to each varying blast
-we rest.—a dream has power to poison sleep;
we rise.—one wandering thought pollutes the day
-we feel, conceive or reason, laugh or weep;
embrace fond woe, or cast our cares away