Are we ever happy?

In sooth, I know not why I am so sad:
It wearies me; you say it wearies you;
But how I caught it, found it, or came by it,
What stuff 'tis made of, whereof it is born, I am to learn;
And such a want-wit sadness makes of me,
That I have much ado to know myself.

          - William Shakespear, Merchant of Venice.

Are we ever happy? Have we ever tried to enjoy our current situation? Does our mind keep wandering away or keep thinking something else? Do we keep getting tensed with our future?
It’s so difficult to understand the human mind. Always unstable, always wandering away. We do not seem to be satisfied with what ever we have. Something keeps worrying us all the time. It’s like while at school, we were so eager to get out of there and go to college. One fine day you finish high school and now you are in college. Just when you are all set to enjoy college life, you find things just do not go your way. Life is tough here too. Then you realize school life was much better. Since you cannot go back to school, you look for other possibilities. The other possibility is getting a job. So we keep thinking college life is bad, getting a job will be the best thing. We will earn our own bread! But once you are out of college and get a job, you realize what you have lost!

What has happened cannot be changed. Time that once went past, cannot be got back.
Just enjoy the current moment and be happy.