I actually wrote a shorter version of this as a comment for lady sun, however, it's been an issue for me for quite sometime.
There are three different levels of desire, I think. The first one, I call it the same, "desire". That's when you want something and try to achieve it. Wanting a new pair of shoes, a red handbag, a new laptop, craving an ice cream in summer, a cup of warm soothing green tea at night, talking to your friend on the phone, ... These can be all categorized as the first level of desire. You want something, and by some effort, spending some time or money, you can get it. The achievement can be as easy as picking up the phone and dialing a number, or as difficult as earning enough money to be able to buy that new piece of technology.
Then there is "dream". Achieving a dream may not be as easy. It may need a lot of effort and also some luck. You may dream to fly to the international space station, or get the nobel prize, or become a bestseller writer. Well it needs a lot of work and effort, sometimes much more money than the price of a laptop, and also the luck of being in the right place at the right time.
If Anousheh Ansari's parents had not moved to US in 1984, I very much doubt that she would have been able to become a space tourist at the age of 40. Rosalind Franklin was not very lucky, so when James Watson used her data to build the model for DNA and then more than a decade later won the nobel prize along with Francis Crick and Maurice Wilkins, she had passed away four years earlier. J. k. Rowling had a strong attitude and a creative mind that turned her to a worldwide known writer. There are lots of other examples.
I think every person needs one or more personal dreams, or as paulo Coelho refers to in his book "The Alchemist", personal legends. They become the reasons a person has to live. Well I'm talking about those who need more than a degree and a marriage and a house and two cars and a bunch of kids to actually live. If one doesn't have such a personal legend, I would say they are just not dead; being alive? I can't say so. But this is another subject for itself.
Going back to the three faces, there is still a third level, which starts as a desire, then turns into a dream, and then after a while, after you discover that it is not just you or even your efforts paired with some luck which can make it happen, it turns into a "regret".
Everybody has regrets. They are parts of the life. They are parts of the bugs in the system (I talked about them in one of my posts before). Sometimes you just put them aside, and forget about them. But sometimes, you come across them every day in your life. They sit there, with a big ugly smile on their faces, making fun of you and your desire to reach them.
...and sometimes it hurts. It really hurts that no matter how badly you want them, they are inaccessible.
I wonder how many people have them, and how often they think about them...