Most viewers initially guess glasses like 3, 4, or 7 because they appear connected. Yet the diagram contains small blockages and interruptions that are easy to miss when scanning the image quickly.
A closer inspection reveals the key detail: every path that seems open is actually blocked somewhere along the pipes. Some outlets are sealed, others are obstructed, and certain glasses have no real connection to the water source.
These subtle blockages completely change the outcome. Despite the appearance of movement and flow, the water cannot reach any of the glasses in the diagram.
The surprising solution is that no glass will fill. The puzzle ultimately tests patience and attention rather than speed, reminding us that careful observation often matters more than quick assumptions.