(Teachings from Gita) One who's not knowledgeable enough thinks that he's the "doer" - the one to perform a given task; but this notion is man-made. Neither does God believe that anybody is behind a given action nor did he create the concept of reward for an action. He also did not designate that a given task will be performed by a given man. It is we who think so. It is we who bind ourselves to the circle of life and death by having a desire for the fruits of our labor and by priding ourselves in being the "doer" of the task. It is our ego which makes us believe that we accomplished a task.
Then what happens to the saying "As you sow, so shall you reap". I always thought it was the guiding principle in life; it motivated us to do good deeds so that we get good rewards. And what happens if somebody does a bad deed, shouldn't he be punished for that? For the common man it still holds true but for the one who wants to transcend to a higher level, it doesn't. As has been oft said, such a man should performs tasks without any pride of being the performer and devoid of any selfish interests like God who created the world and performs all the tasks for it's smooth functioning but doesn't harbor the notion that he's the one who does it.