For each staff id, what is the description of the role that is involved with the most number of projects?
select t1.role_description, t2.staff_id from staff_roles as t1 join project_staff as t2 on t1.role_code = t2.role_code join project_outcomes as t3 on t2.project_id = t3.project_id group by t2.staff_id order by count(*) desc limit 1