Why do some people feel the need to "keep up with the Joneses"?

I’m sure we all know people who like to keep up with the Jones’ of this worlds. No matter how I try, I can’t comprehend it. Especially when they do something that can burden themselves financially or physically or morally.

Do they really not see that it doesn’t make them any happier? I know several people who are very reasonable and responsible people most days till they see or hear someone bragging about something and suddenly they must have it too. I don’t believe its greed or they would just always be on a shopping spree. There desire just isn’t triggered till they personally know someone who has this item. I just don’t understand it and I’m hoping someone on fluther can explain this too me.