Luck is a theoretical concept of abstract proportions and un-contemporary capabilities. It is the absence of skill, yet success is present. It could also be a change or variation of fate where someone receives good fortune.
You're so lucky! I wish I had found $20 on the floor.
No way he could have made that shot! It's luck!
How could he be so good at it? It's his first try... Must be beginner's luck.