Title of this post is inspired by a recent movie, but the judgement drawn here have been used since ages by people in all walks of life, who excel in Chanakya sort of art of negotiations.
The philosophy of 'Kah Ke Loonga' says,
"Know your strengths, & know moral/ethical/social weaknesses of your opponent which he is most afraid of getting public. Let your opponent know from your actions that you know everything about his secrets, but never tell him directly! And turn the game in your favor."
Notice the key point in this philosophy that, you never tell your opponent of your knowledge of what he doesn't want you to know; just act in ways which stimulate his intelligence that, you know everything! This uncertain fear of you knowing everything and possibility of you exposing him, makes your opponent sweat day and night.
Where can we use this philosophy:
1. Politics, 2. Work Life, 3. Negotiations, etc...
Though you may call it some kind of blackmailing, but what is not blackmailing? Is not the customer who starts talking about your competitors' pricing in the middle of sales negotiations, blackmailing you? Is not the conditions and alliances put forth by Powerful nations to smaller nations, blackmailing?
It will not be blackmailing if, the other person is involved in such activities which undermines your sense of worth and do an injustice to you.
Movie from which this phrase has been taken, has a very different take on the practical implementation of this philosophy, which can have dire short & long term consequences too! Controlled use in troubled situations is advised. :)