Zen and the Art of Forgiveness

What does Zen have to teach us? The perfections? There is a difference between forgiveness and forbearance (Sanskrit "kshanti," https://en.wikipedia.org/wiki/Kshanti). But they are often translated as meaning the same thing: patience in the face of difficult people or circumstances. How can we become cool, unflappable, full of self-control (https://wisdomquarterly.blogspot.com/2018/09/how-to-remain-unflappable-sutra.html)? Kshanti is the highest virtue. The Buddha explains in the Dhammapada, Verse 399:

One endures — free of anger —
insult, assault, even imprisonment.
One's army is strength;
one's strength is forbearance:
That person, indeed,
I calls a Brahmin.