I think one meaning is that in order to be good and successful you have to work and its not easy. When you want something, it doesn't just come to you easy as pie. You have to work for it, and have the drive to want to earn it all by yourself. It may not be easy but thats what you need to do to succeed in this big world.
I think that another meaning relates to sports/ coaches. In order for a sports team to be good and successful, the coach has to be mean only to build your team to its highest position possible. Yes, i think this includes making your team do lots of running and work outs. And every player knows that even know it may be hard and tiring while its going on, its all worth it in the end to win it all.
An example of this would be Mr. Macare giving homework. Yes, i know we all love to be complainers and complain about homework. But we all know its only going to prepare us mentally for when we all hit college. He gives us mind work, to make us think in different ways other that just little exercises on paper. Like incorporating art or drawing into an activity. It makes us use both sides of ours brains at once. I don't disagree with the other students, i hate homework, but i just think that it can't always come easy. It will help major in the long run.
I think that this is a very good quote to teach any person at whatever age. It has so much thought and meaning behind it, and it makes me sit and wonder every time i hear it.