Why are we, human beings are never remain happy & satisfied with what we have? Why we always want more? Okay, this is because we are always being selfish. We're never happy with what we have. We get attracted to materialistic things on this earth.
Example, once children had taste a candy, they always want more. When they can't have it, they'll get angry and sad. Even when they have had a million, they soon get tired, they soon get bored and want something else.
Striving for more is a basic human impulse. It's not so bad to have this feeling to strive for more. This striving for more has led the human race to explore the planet, invent much that makes life better.