What is the first name of these people?
SELECT T2.first_name FROM Lessons AS T1 JOIN Staff AS T2 ON T1.staff_id   =   T2.staff_id WHERE T1.lesson_status_code  =  "Cancelled" GROUP BY T2.first_name
first name refers to first_name; people refers to staff related to lessons with a specific condition; condition is lessons with status 'Cancelled';