Sylvia Plath makes use of dark and grim imagery to capture “loneliness”. She suffered from depression most of her life. Her experience is often reflected in her poetry.

The hills step off into whiteness.
People or stars
Regard me sadly, I disappoint them.

The train leaves a line of breath.
O slow
Horse the colour of rust,

Hooves, dolorous bells –
All morning the
Morning has been blackening,

A flower left out.
My bones hold a stillness, the far
Fields melt my heart.

They threaten
To let me through to a heaven
Starless and fatherless, a dark water.