Full Idea
'Luck' is loose shorthand. It stands for various causal chains that intersect and whose intersection we can neither predict nor explain, because we lack the relevant knowledge.
Gist of Idea
'Luck' is the unpredictable and inexplicable intersection of causal chains
Source
John Kekes (The Human Condition [2010], 01.2)
Book Reference
Kekes,John: 'The Human Condition' [OUP 2010], p.13
A Reaction
Aristotle's example is a chance meeting in the market place. The point about 'intersection' seems good, since luck doesn't seem to arise for an event in isolation.