וּמִ֣י יוֹדֵ֗עַ הֶֽחָכָ֤ם יִהְיֶה֙ א֣וֹ סָכָ֔ל וְיִשְׁלַט֙ בְּכָל־עֲמָלִ֔י שֶֽׁעָמַ֥לְתִּי וְשֶׁחָכַ֖מְתִּי תַּ֣חַת הַשָּׁ֑מֶשׁ גַּם־זֶ֖ה הָֽבֶל׃
And who knoweth whether he will be a wise man or a fool? yet will he have rule over all my labour wherein I have laboured, and wherein I have shown myself wise under the sun. This also is vanity.
Read kabbalistic (mystical) interpretation of Ecclesiastes 2:19: and classical mystical sources.