וְסַבּ֥וֹתִֽי אֲנִ֖י לְיַאֵ֣שׁ אֶת־לִבִּ֑י עַ֚ל כָּל־הֶ֣עָמָ֔ל שֶׁעָמַ֖לְתִּי תַּ֥חַת הַשָּֽׁמֶשׁ׃
Therefore I turned about to cause my heart to despair concerning all the labour wherein I had laboured under the sun.
Read kabbalistic (mystical) interpretation of Ecclesiastes 2:20: and classical mystical sources.