Chance is a causally intractable, or as yet a not causally reduced, event in the natural world.
If and when a chance event has an impact on human life (whether expected or unexpected) the event is regarded as a stroke of luck or ill-luck, depending on whether the impact is positive or negative.
Scientifically inclined minds are unwilling or unable to accept that there can be non-causal occurrences: such events strike them as irrational. In the absence of any detectable cause they attribute hypothetical causes to what seem to be chance events.
Thus arose the elaborate pseudoscience of astrology, and the less irrational explanation that luck is a special blessing from an almighty God on select individuals. In the Hindu framework one also attributes unexplainable happy events to benign acts performed in a previous birth: thus assigning a causal link.
Another hypothesis is that aside from the classical deterministic level, the statistical mechanical level of probability, the quantum mechanical level of built-in probability, and the non-tractable level of chaos, there is a hypercomplex level (relating to human thoughts and events). At the hypercomplex level occur utterly unpredictable events.
Call it luck and ill-luck, the people you will be meeting later today or the next week, the newspaper headlines you will be reading next week, and the thoughts evoked by reading this: all these belong to the hypercomplex level of reality.
You may look into my book: Truth and Tension in Science and Religion for more details.
December 25, 2012