Most of us don’t have an advance healthcare directive. Why should we?
Because an accident can happen to anyone, at any age.
Because if you are incapacitated and need medical treatment, this paper specifies who is to make medical decisions for you and informs medical personnel of your end-of-life preferences.
Because if you are unlucky enough to be in the ICU, you are likely on a ventilator. That requires sedation — and a sedated patient lacks capacity. Who makes decisions? Either the person you have specified ahead of time, or the hospital.
Because the paperwork is really quite simple to complete; do a Google search for “advance healthcare directives” and the name of your locality, or look at the websites of advocacy organizations such as Compassion & Choices.