Are expectations a good or bad thing?

I was wondering, if in some cases if people seem more miserable today than in the past. We expect children to study hard and make great grades and make a living, making great money and having a well-paid job. Then there is the children’s version. Get educated and do their dream job that may or may not pay well but somehow they imagine they will have fine cars, fine homes, and live their dream. Then reality hits everyone and instead of feeling on top of the world, they get depressed. And the worse of it is that we all know someone who got what they wanted out of life, and you feel like a failure because it was attainable by someone you know. So is it better to lower one’s expectations in the long run or do you just end up dimming your future with that frame of mind?