Simply experience of earth-centered person. We cannot be sure until we experience it ourselves. But then it is too late. Eternal life is too costly. Everyone dies and leaves their stuff.
Humans are like animals in their mortality.
Note -this is fate of those who trust selves. BUT God will redeem believer's life from grave. Approaching our Redeemer God. A. Be cautious in coming to God. He is far holier than us.