The clam-tower mirage in this verse is the most seductive image in the Wong Tai Sin set: a city floating above the water, towers and markets fully formed, and sailors rowing toward it until it dissolves into green smoke. Drawing this stick for studies means the verse is holding up a particular kind of mirror. The thing you've built is beautiful. The colour-coded timetable, the Notion dashboard, the stack of unopened textbooks arranged by priority, the playlist of lecture videos you keep meaning to start — these are your towers on the horizon. They look like learning. They feel like learning. They are not learning.
The stick is not saying you are lazy or that your goal is wrong. It is reflecting back the gap between the architecture of preparation and the smaller, duller act of actually doing the work. Mirages form when conditions are unstable; in study terms, that often means anxiety. The more uncertain you feel about whether you can pass, the more elaborate the planning becomes, because planning is the part that feels safe. Sitting with one past paper and getting half of it wrong does not feel safe. That is the work the verse is pointing you toward, and the reason the grade on this stick is heavy.