Imagine that a Genie offers you any car in the world. The catch is that it is the only car you will ever own. What would you do?
You would read the manual ten times, change the oil twice as often as required, and you would take fastidious care so that that car remained the car of your dreams forever.
Think about what this tells you about your body.
You get only one mind and one body–the same ones you will have at 20, 40, 60, etc.
Take care of them and maximize their potential. It will be too late to take care of your body and mind (and car) later on. You can maintain them, but it is hard or impossible to undo big mistakes or negligence later on. You do not want to end up with a wreck on your hands.
Your main asset in life is yourself.
Treat yourself as a valuable asset. I often explain to students that I would be willing to pay today for a percentage of the future earnings of good students.
If you value yourself, and invest in yourself, you will be worth a great deal through out your lifetime, both to yourself and to your community.