When you were a child, you didn't know about tomorrow. You were so involved in next moment, that you played ,ate and slept sound. Next moment was certain for you, someone will give food ,or someone will play with you.

You grew and entered class 8th. Now you were worried about certainties of next year. Still you were relaxed that you will enter grade 9 ,no matter what. At this age you started to know the world, hence your vision shifted from worries of next moment to worries of next year.

Now you entered class 12th , and now you are uncertain about your next year....