Lucky numbers or lucky days are indeed just a coincidence of something happening on same occasions.
It's not necessary for something to happen again and again over that so called lucky number/day.
I believe in luck and that it favors us some times but I don't believe in lucky number or day.
It is not bad to believe on such thing and believing in your lucky day could give you a good positive and good mood during gambling session and for me it is nothing wrong to believe in lucky day or number but if it is too much then that is bad, for example wasting so much money for the day you believe that is your lucky day even though you are losing.