A person can then shape his own destiny between his fixed destiny and probable destiny by exercising his free will.

I shall end this by again quoting the immortal words of Paramhansha Yogananda from his Autobiography of a Yogi, which clearly brings into perspective the role of astrology and Karma in our life, "A child is born on that day and at that hour when the celestial rays are in mathematical harmony with his individual Karma, his horoscope is a challenging portrait, revealing his unalterable past and its probable future results. But the natal chart can be rightly interpreted only by men of intuitive wisdom; these are few."

The truly wise man however shapes his own destiny:

Quoting from Yogananda:
"Occasionally I told astrologers to select my worse periods, according to planetary indications, and I would still accomplish whatever task I set myself. It is true that my success at such time has been accompanied by extraordinary difficulties. But my conviction has always been justified; faith in the divine protection, and the right use of man’s God-given will, are forces formidable beyond any other."