From the word "need" you're obliged to do it -- you're forced to do it even if you don't want to, it's not our "want" but come to think of it. Our "wants" are selfish sometimes, it only thinks of our own satisfaction -- our desires, and it's waaaay far from doing what it needs to do. Think of this as an example, "going to school" you NEED to go to school for you to be able to have a bright future and a successful professional someday, it thinks of your future, if you don't want to go to school bc you just want to party all day and this enters your WANTS, you think partying all day may give you a bright future someday? Yes your happy but it is only temporary you know. -Hope it made sense to you, sorry for my bad grammar.