Sometimes you just get your hopes up and POOF, the letdown

I tend to get really excited when I see things going in a direction that will be good, really good for me or us.  I just get right on board. I start to daydream and I really believe that the "change" will take us to a better place then we are. We can finally start to really "plan and get ahead." I believe in the "thing" that I have set my mind to- I believe it is going to happen. I really BELIEVE. Then after the steps that I have put into place are there and I have now focused on the future- things change and don't pan out the way I want or what I thought. I try not to be discouraged or sad or sorry, but the truth is I am. How do I get over these valleys? What have you looked forward to lately and it hasn't happened?