Extensive efforts have been dedicated to developing wearables, but existing solutions focus mainly on feasibility and innovation. Thus, although many devices are named 'wearable', users face some wearability issues. Previously adopted trial and error approaches have effectively produced wearables, but not focusing on human factors. Through an extensive analysis of online comments about head-mounted devices, this paper presents their problem space from a human perspective. The analysis of online comments from existing and potential users enabled us to identify key aspects of the wearability of head-mounted devices, bridging the gap between design decisions and users' requirements.