Causing One To Sin In Middos

Rav Kook ztz"l was a huuuuge chosid of Rav Yisroel Salanter. When the latter passed away, Rav Kook ripped his garment as a talmid does for a Rebbi [even though he wasn't an actual talmid]. But they didn't agree on everything...

There is a famous teaching of Rav Yisrael that in middos there is no לפני עור. This means, for example, that one may praise his friend without concern that it will cause him to be haughty [which according to some is an איסור דאורייתא]. Rav Kook differed. He asserted that it is definitely a no-no to cause others to stumble even in the area of character traits. Please see his Mussar Avicha [3/5] for a number of brilliant proofs from the gemara. See also the Imros Moshe [58] for an interesting disscussion and numerous sources on the topic from the Steipler ztz"l. See also the comment of HaGaon Rav Shlomo Fischer Shlita [Drashos Beis Yishai 49 in the footnote].