According to the Gr”a Zatzal, Sin'as Chinam comes from lack of Bitachon and: הסתפקות being satisfied with what you have. A person who doesn’t have Bitachon in Hashem and Sameach B'chelko is full of Kin'ah and Sin'ah. Believe it or not, this is a lifetime job. A Yungerman told his wife: “If you would be the wife of another person, and I would feel that you are an outsider, I would have Kin'ah”. “But now that you’re my own wife, I barely appreciate what I have, and I take all your Maalos for granted”. This is human nature, and without working on Sameach B'chelko, you’ll spend a lifetime full of Kin'ah for what isn’t yours, and: ממילא as a result, Sin'as Chinam. A Yid has to literally count his blessings and make a Bittul (belittling) against anything that isn’t his.
Spend your life constantly admiring your: wife, kids, job, Kishronos (abilities), house, your unique issues, your aches and pains and friends, your lack of friends, your city (despite all its problems), your Rosh Yeshiva, your Admor, your mistakes and stupidities, your Maalos one by one and keep glorifying every inch of your life and your Mazal (good and bad).
Learn To Hate with A Passion Whatever Hashem Didn’t Give You
And play down and make jokes and Bittulim (belittling) and learn to despise what’s not yours (often even in Ruchaniyus Inyanim) and hate with a passion whatever Hashem didn’t give you (unless you’re working on Ayin Tova, or: קנאת סופרים תרבה חכמה you are using jealousy as a motivation to help you reach higher levels of Ruchaniyus).
