Your will shall apply
Who will take care of your personal affairs once you can no longer manage them yourself? Who will represent you in legal transactions or vis-à-vis doctors if you are no longer able to do so? Can you still make a will yourself if you are no longer able to judge?
As long as we are in good health, such questions hardly worry us. Often, an illness, an accident or even just the fact of being single is the decisive factor in dealing with getting older and making the necessary preparations.
If you conclude a universal power of attorney and a preventive care agreement at an early stage, make sure that you are represented by the person you appoint should you no longer be able to make decisions yourself.