Rav Yisrael Lipkin of Salant said “that perfecting one character trait is more difficult than learning all of Shas (the entire Talmud)”.
It is known that often Rav Yisrael would attend shiurm given by the Chidushei HaRim, Rav Yitzchak Meir Alter, who was the first Ger Rebbe. The Chidushei HaRim was known for finishing all of Shas every month, in depth. It is also know that he spent seven years working on the middah of having an Eyin Tovah (seeing the good in others). Parhaps the Chidushei HaRim’s avodah was what prompted Rav Yisrael to make the above statement?