It's not our circumstances that steal our joy; it's our attitude during our circumstances.
It is easy to think "If I could just get a new car, a bigger house, a better job, or more money, then I'll be happy." We tend to view happiness as a commodity attainable by wealth. However, as the old saying goes, "money cannot buy happiness."
Indeed, no amount of money or things will ever give you lasting joy or contentment; that's because joy and contentment are not based on circumstances. Therefore, if you're not content with what you have, you won't be content with what you want.
Although at first it may seem difficult, it is very possible to be content even during harsh circumstances. Paul said, in Philippians 4:11-12, "I have learned to be content whatever the circumstances. I know what it is to be in need, and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want."
In those two verses, Paul is saying that he could be content—that is, have joy—regardless of his circumstances. Joy should not be dependent on circumstances; it should be present regardless of them.
When Paul said that he could be content "in any and every situation," he truly meant everything—even the tough times of testing. In 2 Corinthians 11:24-27, he lists some of the tough times that he has endured: "Five times I received from the Jews the forty lashes minus one. Three times I was beaten with rods, once I was stoned, three times I was shipwrecked, I spent a night and a day in the open sea, I have been constantly on the move. I have been in danger from rivers, in danger from bandits, in danger from my own countrymen, in danger from Gentiles; in danger in the city, in danger in the country, in danger at sea; and in danger from false brothers. I have labored and toiled and have often gone without sleep; I have known hunger and thirst and have often gone without food; I have been cold and naked."
Even in all these things, Paul had "learned to be content." Clearly, it's not our circumstances that steal our joy. You, too, can learn "to be content whatever the circumstances."
Stop thinking that you will have joy after you buy a new house, after you get married (or have children), after you buy a better car, after your in-laws treat you right. Don't put off joy until after everything goes your way; decide to have joy now! For you can have joy whatever the circumstances!