NET
12 For no one knows what is best for a person during his life—during the few days of his fleeting life—for they pass away like a shadow. Nor can anyone tell him what the future will hold for him on earth.
Darby
12 For who knoweth what is good for man in life, all the days of his vain life which he spendeth as a shadow? for who can tell man what shall be after him under the sun?
KJV
12 For who knoweth what [is] good for man in [this] life, all the days of his vain life which he spendeth as a shadow? for who can tell a man what shall be after him under the sun?