'Shadow' in the Bible

For who [limited by human wisdom] knows what is good for man during his lifetime, during the few days of his futile life? He spends them like a shadow [staying busy, but achieving nothing of lasting value]. For who can tell a man what will happen after him [to his work, his treasure, his plans] under the sun [after his life is over]?

But it will not be well for the evil man, nor will he lengthen his days like a shadow, because he does not fear God.