Why is it difficult to learn to be happy with what we're given? We live such blessed and full lives but yet we always want just a little bit more. I'm sure we've all used the phrase; "The grass is always greener" in reference to wanting something somebody else has... But sadly, this is the way a lot of people look at life. They convince themselves that - though things aren't exactly how they want them to be, it's just the way it has to be and they need to learn to live with it... Now it's probably safe to say that we won't get everything we want in our lifetime, but having the "I just need to learn to live with it" outlook won't allow anyone to be fully content with their life. As Christians, it shouldn't be a motto we live by..
Going along with that - however - a common misconception is that contentment is automatically tied to Christianity. But we should realize that contentment is something to be learned, sought after, and gained. - It's not just given to anybody who decides to take on the the role of a disciple of Christ. However, I believe that once we take on the responsibility of being a Christian, we have no reason to NOT be content with our life. We've made the most important decision that we'll ever have to make and if we continue to live like and for Christ, we should be happy.
When I think about having a happy and fulfilled life, I think about Paul and the trials he faced. And even though he went through some horrible situations, he was able to remain content. He tells the church at Philippi that he counted everything as loss in order to gain Christ (Phil 3:5-8). He also had a firm grasp on the fact that earthly things are quickly passing away... In 2 Cor. 4:18 he writes, "As we look not to the things that are seen but to the things that are unseen. For the things that are seen are transient, but the things that are unseen are eternal." For me, this is a difficult concept to grasp and hold on to. And again, I think this is why so many people are unhappy - because it's so much easier to focus on things like being better looking or having better jobs, fancier cars, more money, etc because it's right in front of us. But we have to remind ourselves of Paul's words listed above and in 1 Tim. 6; "Having food and clothing, with these we shall be content."
As Christians, we know what's truly important and that we have no reason not to be happy if we're living right spiritually. We need to remind ourselves of that.