אִם־אָ֭מַרְתִּי אֲסַפְּרָ֥ה כְמ֑וֹ הִנֵּ֤ה ד֭וֹר בָּנֶ֣יךָ בָגָֽדְתִּי׃
If I had said: 'I will speak thus', Behold, I had been faithless to the generation of Thy children.
Read midrashic interpretation of Psalms 73:15: and classical rabbinic exegesis.