In "The Plain Sense of Things," Wallace Stevens writes "It is difficult even to choose the adjective / For this blank cold, this sadness without cause." That first thing that popped into my mind from this line was 'depression.' You could say that the entire poem relates to depression, sometimes its a stretch. Looking at the first stanza, it can be describing autumn when the leaves fall. So after the leaves go away, all that's left is the trunk of the tree and the branches, the "bare bones." Leaves can represent life and energy and movement, and without that, life is unenergetic. Life becomes stagnant in the winter.
Second stanza: sadness without cause = depression. "The great structure has become a minor house." This is saying that what used to be grand and wondrous and exciting is now just minor, comparable to when you become depressed, everything you used to get happy and excited about is just one more plain old thing, very uninteresting. I have no idea what the last line in that stanza means.. maybe the line is supposed to be so out there and weird to say that creativity and imagination is dead? That's a stretch.
Next, the poem talks of things in disrepair, in a state of complaint, seeing everything as negative. It talks of failure and how everything is a repeat. When you're depressed you kind of go through normal life on autopilot and life just becomes a routine you have to go through.
Further in the poem, "the great pond and its waste of the lilies" : the lilies are a waste because beauty goes unappreciated during depression. And the last two lines convey the idea that creativity and imagination are required.