Ecclesiastes 2:19

2:19 Who knows if he will be a wise man or a fool?

Yet he will be master over all the fruit of my labor

for which I worked so wisely on earth!

This also is futile!

Ecclesiastes 11:6

11:6 Sow your seed in the morning,

and do not stop working until the evening;

for you do not know which activity will succeed –

whether this one or that one, or whether both will prosper equally.