That TV show that you really feel like watching will be of no use to you.
That friend whom you want to go out with will not be making your dad and mom proud.
Be Selfish.
As you move forward in life, you will realize that being Selfish is really important. Nobody really cares about you other than you.
Study because one day you will know that Knowledge is power.
Don't study because you have to get good grades. Study to be really good at studies. To gain knowledge. There will be times when you will feel that its of no use but after some time, you will know that you are smart because you kept studying.
You will never get back this time.
Enjoy studies. I mean really enjoy it. Find happiness learning things. Right now as you read this, you learned something. It's making you better day by day.
Understand that when you study or exercise your mind, you are getting better. People who stop studying after 22 know that their minds are no more getting exercise, they find it difficult to remember things, to memorize things, to find the answer of 9 * 24 becomes difficult.
Give up on everything around you. Just know that at this age, at this time, studying is the only option you should have in life.
All the best.