a job with different tasks or more variety requires more concentration, i.e. 'work' or disruption of ones' mental 'rhythm'
this theory could be PART of a job granting one a PERIOD of repetition OR; the entire day of repetitive task/s.
this idea could be experienced in assembly line type jobs, or jobs which entail tasks that always remain pretty much the same.
mike foolsley dumped a whole pile of new orders on my desk, completely different then last week, disrupting my worker's rhythm!!
working this job is no problem! i've been doing it so long, i just go into a worker's rhythm TRANCE!