Before revision:  The difficulty is rooted in the fact that a job with multiple tasks is considered complete only when all of its tasks complete processing; i.e., the job response time is the maximum of the response times of its tasks  , which is hard to analyze since these task response times are generally not independent.
After revision:  The difficulty is rooted in the fact that a job with multiple tasks is considered complete only when all of its tasks are completed, so the delay of a job is the maximum of the response times of its tasks , which is hard to analyze since these task response times are generally not independent.