Many people don't see the difference between desire and attachment, so let me give you an example. You are on your way to work, and you usually catch the 8:17 train. You wish (desire) to catch this train because it gets you to work a little early, allowing you time to get situated before starting, maybe get a cup of coffee. Today, there was an accident on your way to the train station, and you ran late and just missed the 8:17.
Now the average person, someone attached to results, would get upset now. There is another train at 8:26 which can still get you to work on time if you hustle, but this means you don't get your morning cup of coffee, and you will start the day hurried and frazzled, and this would upset the average person. You would not be upset because of losing your desired outcome, but because you are still attached to that outcome and the experiences that would have resulted from it. Attachment is an emotional state that draws you out of the Present Moment and into the imagining of outcomes which are no longer possible. It is a clinging to the past.
Now, a more "evolved" person can still have desires, but can let go of unmanifested experiences. Take our example. Instead of becoming upset at having to catch the 8:26, you can look and see that no actions of yours could have kept this experience of missing the 8:17. This can now be seen as an opportunity, because no circumstance happens "by chance". Any situation which comes to you not of your active choosing is a situation drawn to you by your soul or higher self, for the purpose of setting in motion a new set of circumstances. Thus the missing of the train can be released, and you can now look around at your new experience and try to find why it has come into your life. Sometimes, such events are the triggers for serendipitous coincidences (what Karl Jung called "synchronicities"), initiating new possibilities.
Thus it is possible to desire an outcome but not be attached to it if it does not manifest.
