In the future, we shall know the exact moment of our death, because we ourselves will have picked it. Thanks to advancement in medical science, it will be possible for people to live hundreds or even thousands of years in relative good health. But, for many, this greatly expanded lifespan will be a burden rather than a blessing. There will be little incentive to accomplish anything when you have a near-endless amount of time to do so.
Instead, many will choose to program into their genes and exact day of death. Some will want to live long, leisurely lives, but others will find more incentive to live under a literal deadline, with just a few decades or even a few years to complete all they must.
On the day they have chosen to die, they will gather friends and family for a party, and will make a list of all they had done, and all they wish they had done. And then they will walk into the woods to be alone, and to wait for the end.