Nice question. Every human has asked this question at some point of his life .

My spiritual mentor (Bano Qudsia, also an author ) wrote something very interesting about this topic. She said that everything in this universe is created in pairs like man and woman, night and day, good and evil, mountains too have pairs, even good and bad blood flowing in our hearts are paired together.

Electricity can't be produced just by positive current, for it we need negative current too, Similarly luck and human will are a pair. They run parallel on the track of life and whenever they converge together, A current is created, Sometimes it is the current of success and sometimes of failure. But whatever we get in our lives it is because of convergence of human will and luck .