A lot of people are wildly optimistic about some coming development in their lives. At least they are today. Tomorrow, they may swing wildly to the other side of the spectrum, based on little data, or even based on the absence of data. ("They didn't call back; they must not be interested.")
Why do people change their opinions on something so quickly? I submit that it has a lot to do with a lack of perspective. If you don't have a grasp on the big picture (your long-term plans), the little things are going to run your life. And those little things are appallingly little- the lack of a phone call, or an inflection in someone's voice. An eyebrow.
I have a few ideas on how to combat this problem, to come in the next few days.