The doctor tells you in 20 years you will need neck surgery. He's replaced a vertabra in your neck and added a metal plate as a result of a car accident, and you are doing great. But there's that picture of the future he's planted in your head.
Your former life was about trusting your body. You could make it do anything you wanted. And now, an expert has told you that you can't trust it anymore. Avoid anything that involves up or down motion. Don't carry heavy things.
So what happens? You begin acting like the surgery is every day of your life. You let the expert hold you back. You limit your choices and you feel like you have already aged by those 20 years. You focus on what you've lost and not on all that you have gained. The pre- and post-event differences become all too real.
The only future that any of us have is today. Right now. If we don't live that way every single day then we will have wasted today and every day between now and that 20 years. No one, not even an expert Doctor (who made miracles happen) can tell you how to live your life or can take away the joy of experiencing every special moment.