The harm of doodling on the blackboard

The blackboard is used by the teacher for lectures, so naturally it can't be scribbled. Graffiti is disrespectful to a teacher, just like scribbling on a teacher's textbook.

waste time/waste of time

If you scribble on the blackboard, the teacher will walk into the classroom before the scribbler erases the graffiti, which will delay the time of the teacher and classmates.

Increase the amount of labor

Graffiti on the blackboard will increase the workload of students on duty. Usually the students on duty clean the blackboard after class. If someone scribbles after the students on duty clean the blackboard, it will inevitably increase unnecessary labor for the students on duty and affect unity.