Some people say a person's destiny is pre-determined and fixed, and there is nothing one can do to change it. Other people say destiny is completely malleable and entirely in our hands; that our choices and thoughts determine where we end up. Which view is correct?
Yoga says both are true: We have a destiny, and we can change it.
We come into this world bearing a hidden reservoir of subtle seeds, called Samskaras, that, when they burst forth later in life, predispose us to have certain interests, certain life-experiences. Although we are not consciously aware of these Samskaras, they pull us toward our destiny. Yet even though we have predispositions, we can change our course.
The first step is to become self-aware, so we can witness our own actions, and see the direction we're heading. Often, this takes a "wake-up-call", some painful experience, to motivate us to pay attention. Until then, we live unconsciously, acting out our predispositions. Until then we drink to excess, or worry ourselves sick, or in any of an infinite ways harm ourselves, and then by some good fortune we wake up, catch ourselves in the act of harming our life, and have a chance to correct our ways.
Practitioners of meditation don't wait for a chance wake-up call. As part of their spiritual practice they cultivate their awareness, and learn to witness their own thoughts, emotions, and actions.
However one wakes up, doing so offers the chance to alter our destiny.
Those who stay asleep, who refuse to wake up, are destined to repeat the same mistakes, over and over, leading themselves evermore into pain. Those who wake up, have an opportunity to diminish the pain they encounter. The Yoga Sutras of Patanjali tell us that "The pain that is yet to come can and should be eliminated". Becoming aware of our thoughts, emotions, and actions is the first step toward doing so.
Once awake, the next step is to exercise our will, and take action that leads in a better direction. Because our every thought and action creates new Samskaras, by exerting effort to act differently than our initial tendencies, we create new subtle mental patterns that, when built up and strengthened by repetition and focus over time, slowly change our tendencies, and we become different. Over time we decrease the pain in our lives.
With sincere and regular practice we can change our destiny. As the great Himalayan adept, Swami Rama, said "You are the architect of your life and you design your destiny."