We are disappointed. Often.
I think we can narrow the cause of our disappointment down to two things:

1. Things change. People die, money goes away, new loud neighbors move in. We don't like things to change, because we really like the way things are. Even if we're miserable, we'd rather maintain the status quo than have things change.

2. We have a lot of expectations for how we want things to turn out. And then, on top of our fantasy idea about the way things should be, we are attached to the outcomes we created in our minds. How silly is that?

Think of the last time that you had an expectation about something and it didn't turn out the way you had hoped or...expected.
Mine was today. I planned to take an amazing bike ride (my first of the season) 7 miles to teach yoga in 80 degree heat. I expected that it would be awesome, like a Coca-Cola commercial. Me all sexy and tan with a big smile and some awesome song in the background. Truth is, I got my ass handed to me. Which was just another way that things could turn out, and did turn out.

Think about the last time you didn't have expectations. What happened?

For me it was going to India. I had no idea what I should expect. I had some relative notions about possible experiences (lots of beggars, lots of trash, foreign language, big cities) but no clear fantasy projection about what I wanted to gain. I didn't know if my program would be any good, if Indians would be nice, if I would be afraid while I was there. And it turned out to be one of the best experiences of my life.

I wasn't afraid the whole time.

I'm not saying this is always the case, but setting yourself up for each and every situation with a grand expectation is a great way to disappoint yourself. Often.
Instead of constantly comparing the way things are to the way you would like things to be, can you instead appreciate things for what they are?

Here's a meditation to help with releasing your attachments and expectations.
Bring your awareness to the crown of your head. Rest attentively there keeping your body relaxed and your breath steady. With each breath, increase your point of awareness at the crown of the head and increase the vibrancy of that feeling. (2 minutes)
Now begin to draw your breath from the crown of your head through the middle of your brain to your heart center on an inhale. Exhale stay present in the heart center. Inhale back up from your heart center, through the middle of the brain to the crown of the head. Exhale up and out of the crown of the head. With each continuing breath, increase the awareness and vibrancy of the points at the crown center and the heart center. (3-4 minutes)
Now, maintaining that same pattern of breath, begin to draw in your goals and desires from the universe from the crown through the middle of your brain to your heart. Exhale let your desires rest in the heart. Inhale moving from the heart to the crown, drawing upward your expectations and any attachment you have to the outcome of your goals and desires. Exhale release them into the universe through the crown of your head. (3-4 minutes)

Try it out. But...try not to have any expectations around it. Let it unfold naturally and be open to the possibilities that it presents.