think about it this way
if you got the same wage as everyone else, regardless of your occupation, you wouldn't bother getting educated/specialised to get higher paid jobs would you?
Also, if your colleagues were slacking off (being unproductive) while you were working hard and being passionate about your job while getting the same wage, you would probably slack off too.
what does this lead to? an increase in overall inefficiency of our use of factors of production
BTW. i dont remember that being in prelims? but then again, its common sense, so I guess you should know