Buddhism explains destiny through the concept of karma. Karma originally meant action. Later it came to be understood as the destiny one had created through these actions. Every thought, word and deed is a cause which creates an effect. On a simple level, if we go to work, we will get paid, if we exercise, we will become fit. Buddhism therefore teaches that our fate is not arbitrary, neither is it imposed by supernatural forces.
Nichiren Daishonin stated: "If you want to understand the causes that existed in the past, look a the results as they are manifested in the present. And if you want to understand what results will be manifested in the future, look at the causes that exist in the present."
The workings of cause and effect may not be immediately obvious. Very often life seems unfair. How is it that an unscrupulous and selfish businessman can become so rich? Why is it that the nice woman down the road has cancer? Why are people born in such different circumstances? Surely a child has had no chance to make the causes to be born into poverty and hunger?
The concept of karma is based on the understanding that life is eternal. Circumstances of birth are therefore determined by causes made in previous lifetimes. The law of cause and effect is exact. We may be able to escape detection from the laws of society but there is no escaping this law of causality, which is etched indelibly in our lives. Although it is strict, it cannot be said to be unjust. It certainly gives a logical explanation for our differing circumstances of birth. Furthermore, it is an optimistic teaching, because the power to create destiny lies in our own hands.
On face value, the law of causality may sound moralistic, but it is much more complex than a straight moral code. Science, of course, recognizes cause and effect. However, science has discovered that the effect of a cause cannot be predetermined: the effect of a particular cause depends on the influence of many other factors. In a similar way we cannot say that the nice woman down the road getting cancer is a result of her being a terrible person. It may be that she is very caring and helps other, but she is also extremely worried and, in her case this unease of mind and body has manifested itself as cancer.
It is impossible, also to look at effects and label them as good or bad. Some people who discover they have cancer develop a fighting spirit and a new appreciation of life. These people are truly creating their own destiny, through their spirit to live now and for the future. This is the spirit of Nichiren Daishonin's Buddhism.
In the West, we have received the impression that karma is fatalistic and fixed. However, the reverse is true. Because we take full responsibility for our own actions, and therefore our own results, we are empowered to seize our own destiny and change it for the better.