A student asked his teacher, "What is greed?" The teacher said, "In order to answer your question, go through the chocolate factory next to our school and pick the one chocolate you like the most. but there is a rule. as you pass through the factory, you can not turn back. you must pick the chocolate as you go forward only."The student went to the chocolate factory. As he walked through, he saw the one chocolate wrapped nicely, he instantly liked it but he wondered that he may find much bigger one further. So, he walked further, then he saw another chocolate. But again, he thought the same. When he started to reach near the end of the factory, he couldn't see any chocolates as big as the one he didn't pick earlier and started to regret his decision of letting it go. Finally, he gave up. He went back to the teacher with an empty hand and gave an explanation of what he did. The teacher told him, "You did like the one chocolate very much but still you kept looking for a bigger one. and later you realized that what you let go off was the best chocolate you could find there. that my dear is called greed." 
We let go of many good things in our life because of our greed of having even better things. Our human nature is such that we always want better and better. But in the search of better, we let go of many good things which could have given us similar satisfaction and made us happy. Learn make your choice wisely. 