I too have heard this b4, however one can not say enuf that it doesn't hurt to make sure u have ur priorities straight.
Otherwise the little things take up too much of ur life, and u have to get rid of lots of pebbles (even more sand )to make room for one more rock.
The version I read had this at the end : After the Professor had filled jar with rocks, pebbles and sand, a college student poured some beer in jar and said ; " Remeber when u think ur life is full there is always room for a beer" lol <img src=icon_smile_big.gif border=0 align=middle>