What's the difference between isolation and suffering? In "There's a certain Slant of light," the two may look the same, but they're depicted by the speaker in slightly different ways. Isolation is kind of the precursor to suffering in the poem. Think about it: without isolation, suffering doesn't happen (at least not in this poem anyway). That's not to say they don't have lots in common, and lots to chat about together. For example, both appear to be illuminated by that mysterious slant of light.
Let's see…where to place all this blame? The speaker's suffering in Dickinson's poem is brought on by both the outside and inside worlds since the "imperial affliction" is sent from the "Air."
Cue the "Unsolved Mysteries" theme song. Even the speaker's suffering is depicted in a mysterious and understated way that's not overly emotional or specific about its origins.