In reality, what people are denying is that outside factors affect luck, and to this point I will not argue today. Instead, I will merely prove that you cannot deny luck, and toss this into the bin of clear, and widespread misconceptions.
Luck is defined as "Success or failure apparently brought by chance rather than through one's own actions". To examine luck, we must examine chance. Chance is defined as "a possibility of something happening". There is nothing supernatural to it, as is often suggested.
Luck is completely random, and there is no evidence of anything that can affect luck besides cheating (which in reality, by bringing in a human element takes away the element of luck), but luck is undeniable. The luck that any random number could be picked for the lottery. The luck that gives a millionaire lawyer, and an impoverished immigrant completely equal odds. The randomness is what luck really is.
So, while people say "Oh, I've had good luck" or "Oh I've had bad luck today", they are in reality saying meaningless sentences. Luck is the element of chance, and therefore I don't think there can really be "good luck", and "bad luck", so much as "a bad outcome when left to chance".
So in conclusion, luck is involved in everything beyond our control, but there is no magic to it, and you cannot control luck (or else it is not luck at all, due to the human manipulation). Can luck really be defined as good or bad? What do you think?