Woe to a man who is unaware of his faults, he is not attentive to what needs repair.
But double woe to he who is unaware of his virtues, he is unskilled in the tools of the trade!”
Where is this quote of Rabbi Yerucham Levovitz?
According to Aish, the quote comes from Rabbi Yerucham's Even Sapir, pg. 72:
"אמר הגאון רבי ירוחם ממיר (בספר 'אבן ספיר' עמוד ע"ב): "אוי לו לאדם שאינו מכיר ליקויי נפשו, שהרי אינו יודע מה עליו לתקן... אבל, אוי ואבוי לו לאדם שאינו מכיר את מעלותיו - כי הן אפילו את כלי עבודתי אינו מכיר"."
"Rabbi Yerucham Levovitz zt'l said: "Oy (woe) to he who doesn't recognize his faults. But oy vavoy (double woe) to he who doesn't recognize his qualities because even the tools of his trade he doesn't have." (from Alei Shur)
His talmid, Rabbi Shlomo Wolbe zt'l explained: Every person is given a special trait or quality that with this trait he can change and transform himself completely to the good - and this is all of a person's job in this world, because through this he will reach all of his perfection - and this also applies for the negative side (i.e. to turn away from one's special negative trait). (Alei Shur shaar 3 pg.146)
It's likely that Rabbi Wolbe, being a student of Rabbi Yerucham, heard it directly from him and not from his book.