Dreams.

...Everyone dreams! But I'm sometimes surprised by how simple some people's dreams are – some want money, others want girls. Maybe that's a good thing in some ways, but when you completely achieve your dream, it stops being so desirable! And you just get bored... It's better to dream about something spiritual! About something that can't be taken away.
One example from the Heroes theme – remember the "dragon slayer" campaign? Darcon wanted to kill the Azure Dragon and become famous for all time. But what happened in the end? When he defeats the great monster and realizes that he has achieved his life's goal, what does he feel?
"My dream seems illusory. I thought the dragon would be the key to paradise in the south. I am confused about what will happen next? My disappointment is growing..." - a quote from Darcon's words (John Van Caneghem?), no comment...
And I'll say that a person is happy not when they achieve their dream, but when they strive for it! But few people know how to notice this happiness...