Japanese values human relationships very much.
Once if they got helped or receive favor by someone, they will never forget the kindness .
(Of couse many people who help or give favor don’t expect your return.)
For example, in my case, When I start up my business, Mr.S introduce some customers.
Thanks to his introduction, my business spread and I could get profit.
If there aren’t his introduction, I might not succeed.
So if Mr.S have some trouble, I will do everything what I can do.
Japanese especially think about what they can do for thire benefactor.
It becomes a matter of course.
So if you return evil for good, you will be criticized intensely.
To return evil for good is most disliked in Japan.
The kindness is the best present for us.
If you don’t have personal magnetism, you never get any kindness.
So it is no exaggration that your success depend on someone’s kindness.
In other words your success depend on your personal magnetism.