Luck is generally said to be blessings of God. It is also similar to Bhagya, Kismet, Fate etc. but differs from these in a way that it is sudden, by chance that something good or bad happens in one's life. Now the question is, "Why suddenly Luck shines on a particular person & that person wins a lottery?" To understand this we need to understand the Hindu theory of Karmas.
As per Bhagwat Gita, individual soul is immortal & is capable of taking rebirth in different bodies after it leaves one body at death. As per the Hindu Philosophy, 'Actions or Karmas' of previous birth become the basis of this birth & Karmas of this birth become the basis of next birth & so on. Every Karma has a consequential Fruit related to it. A person has to enjoy the good or bad fruits of "Karmas", in his/her next births. Karmas done by a person, remains with that person, unless he/she has enjoyed the consequential Fruits arisen out of doing that Karma.
At the death of a person, individual soul takes with it all the accumulated Karmas, which contain Karmas done in this birth & also the Karmas from the previous births for which its fruits are yet to be enjoyed . Now when a person gets something by chance, it is the outcome or fruits of previous births Karmas which are bearing fruit now. So when a person suddenly wins a lottery, then at that time some very good deeds or Karmas of previous births suddenly bear good fruits. Similarly when a person gets sudden loss in life & have a bad Luck, then also some bad deeds or Karmas of previous births suddenly bear bad fruits.
So this explains all such events as per the Hindu Philosophy. It is also due to good & bad Karmas done by an individual in earlier births only that a person is born in a rich or poor family. All inheritances too can be explained like that only. So let's all do Good deeds or Good Karmas only so that our this & next lives can be good.
Read also: What is Karma?