You are talking about the outcome after you gamble. And it's very easy to know that you've been lucky when you had won a lot in the end of the day. There's no way to identify and figure out if you are lucky for this day. The only way to know if you are lucky is to have a gut feel that you will be lucky and have a good day.
That is right, you will not know when you will be lucky or unlucky, you will just realize it after you think of it in the end of the day. Gamblers usually look at their balances after leaving the casino or a gambling site, most of them will say when they lost a lot, it is an unlucky day, with a lot of win, lucky day. But the luck of person sometimes was just for one point, for example you was promoted, the same time your salary was raised unlike the old members at your new position. But then when you gamble, you will not be having the same luck as what happened.
Lucky or not just do your responsibility as a gambler and do your own wise decision as you gamble. Withdraw when you've got enough already and forget, stop on the said day and just take a rest for the next hours. Luck is just passing by and we can't even notice on how long and how fast it is going to get through to us.
Always start your gambling with positive mind then you will get a good result. But in gambling luck is like passing cloud it will come and disappear. So you will get to know when is your lucky time that time to make money and when your bad time started to stop your game and withdraw your winning. Don't believe that luck will come once again it won't come.
If having a positive mind when starting a gambling game means a good result then most of people who are into gambling would have been seen a good result in their life. I think this kind of stuff is a fallacy, a wrong belief since when you play a gambling game, it all random. An external factor will never affect the result of the game since the result is based on the internal setup of the game.