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I guess Action (Karma) is the Key because everyone know about his/her good & bad intentions but still performs that action.

Yes. Sometimes human have to perform some actions irrespective of his/her good or bad intentions. But to have a good intention is also a part of good Karma. If your actions and intentions go in sync(considering good intentions), then you are on the right path of Karma.

Yes you are right. Intention is a part of Karma.