What is with dreams?

What is it with dreams? Why we dream? Why we try to achieve something, which is vague at times? And when these dreams gets shattered, when we fail why we get mocked? Wasn't it was told to us that dreams are important? 

Then why mock when ones dream gets shattered. Since last two weeks I have seen things happening to some one else which happened to me some years back. There are similarities and I saw the desperation on that man's face. He reminded me of days when I faced uncertainty, gloom and was almost perished. Don't want this guy to meet his nemesis so soon. Don't want him to loose out because he dreamt.