Lyric discussion by BlckDeth 

Cover art for The Raven lyrics by Alan Parsons Project, The

I think that the Raven personifies Doubt. The way that it is ever-present in the background, yet always shrouded with nets of shadows, strengthens this claim. Doubt is also removed only by our own actions, thus the line, "no words can soothe him, no prayer remove him." When the Raven speaks of "Nevermore," he is saying that the opportunities to rectify past doubts are long-gone, and that there is nothing that can be said by any man to soothe the what-ifs of our past.

@BlckDeth It could be the case, and in fact my own interpretation was depression, rather than doubt. But if you go and read the poem, it opens your eyes as to what it really means...