Life of everymen in earth is pre-determined including his happiness, wealth, marriage, children, occupation, death etc. there is a Tamil proverb saying
விதி வலியது, விதி வழியே செல்லும் மதி
Vidhi Valiyathu, Vidhi Vazhiyae Sellum Mathi
Fate is powerful and your mind follows your fate and acts accordingly. You can never act against this law of nature. Destiny of every man can be predicted to some extent with the help of Vedic shastras like astrology, palmistry etc.
Nature is powerful. Day and night, joy and sorrow, birth and death are a part of cosmic plan. You can never act against the law of nature. But still, man has been created to live in harmony with nature. If everything happens as pre-destined, then there is no purpose in being born as a human with sixth sense and intelligence. God did not send a problem to earth without a solution for it. There is a proverb in Tamil saying
Vidhiyai Madhiyal Vellalaam
விதியை மதியால் வெல்லலாம்
You can have victory over your destiny with your intelligence. Though you could not change your fate completely, you can shape your destiny to some extent by following Vedic remedies suggested by saints of different religion. Different types of vedic remedies includes Mantra, yantra, tantra, gem theraphy, rudraksha theraphy, colour theraphy, vasthu, puja, homa etc.