When you see pictures of Taylor Swift and her #squad vacationing in Hawaii or Beyoncé sharing another one of her catalog-worthy vacation pics, we can't help but feel envious. After all, we can't afford those trips, or at least not dozens of them in a year. But believe it or not, there's a depressing side to celebrity globe-trotting. Although their lives seem exciting to us, famous people who are used to traveling all the time can sometimes find it boring. Psychologists call this the "hedonic treadmill," which means that people always return to their normal levels of happiness regardless of what happens to them. So, for example, taking your first ride in a private jet might seem fun at first, but after a while, you get used to it. 

"I can't buy happiness anymore," internet personality Dan Bilzerian once said. "I've bought everything that I ever wanted. There's not really anything I want anymore."

Wow, depressing much?