Deal With Others as They are Now
In your relations with other people, live in the present. Reviewing past misdeeds and failures of the people you associate with just adds fuel to the fire of resentment. Try to deal with people the way they are now. True, they might have offended you in the past, but what do you gain by thinking about it now?
If you find it difficult to stop thinking of others’ past offenses, write a list of what you gain by thinking of that past, and another list of how you lose by doing so. When you see the harm you are causing yourself, you will be more motivated to let go of the past.
(Rabbi Pliskin’s Gateway to Happiness, p.146)