A more accurate definition of Intelligence?

In my academic career, I have always had one immovable rule: do everything.  I never considered the option of whether to do homework or not, only when to fit it in.  I have always just done everything without really thinking about it.  Today however, I began to consider a different course of action.  I was assigned a writing assignment in my Oceanography class that, although not very difficult, will probably take me 1-2 hours to complete.  The assignment is only worth 10 points, the same amount as all of the other homeworks I have completed during the semester.  When I saw it, the first thing that came to my mind was "I really don't feel like doing that, but I guess I'll do it anyway."  Then I realized, maybe I don't have to!  I have been a little stressed out lately and have a lot of stuff to complete for other classes in a very short amount of time, so adding another little assignment isn't exactly appealing.  This class has been a fairly easy, low maintenance class most of the semester, and I have gotten A's on pretty much everything we have done, including tests, and even have some extra credit.  So I figured...maybe I should look over the point totals and see if this assignment is really necessary.  Upon some inspection, I discovered that if I didn't complete the assignment I would still receive an A in the class even if I get a C on the last test, which isn't very likely.  SO...researching and writing it would cost me a couple hours of time without an noticeable gain.  Isn't the smarter thing to do in this situation dedicate my time to the other work that actually matters??  I think...although contrary to all other previous beliefs of mine, that the SMARTEST thing to do, is only what is necessary and beneficial, not everything.