College A professor tells the class that they will be performing an experiment the next day. When the students get to class, they see the professor with a large glass vase, some large rocks, some small pebbles, and some sand. The students all get seated, and the professor begins the experiment. He fills the vase with the rocks and says, ""How many of you says this is full?"" When half the class raises his hand, he nods, and then pours in the pebbles. ""Now how many of you says this is full?"" When no one else raises their hand he adds the sand and repeats the previous question. The rest of the class raises their hands. The professor then sits down to begin the rest of the class, when a student walks up with a bottle of booze that was in his backpack. He pours the booze in the vase and says to the professor ""Now what does this teach you?"" When the professor didn't answer the student said ""There's always room for beer.""