Well, sometimes it's the unique setting or the unexpected plot twists. Maybe the boring man gets involved in extraordinary circumstances that make the story exciting. Also, the art style and the way the story is told can add to the appeal.
It could be the depth of the character's inner thoughts and emotions. Maybe the story shows how he overcomes his boredom or finds meaning in unexpected ways.
The interesting part could come from the development of the character. Seeing how a seemingly boring man transforms or has hidden qualities revealed. Or it could be the exploration of themes like self-discovery and finding purpose that draw readers in.