Coincidence or not, it seems the whole world was built around this number. But do you know why?
7: The Perfect Number
In almost all cultures of the world, the number 7 is portrayed as the number of perfection, peace and of course luck.

Hindus believe that humans have seven energy points called chakras. The ancients believed that souls ascending to Heaven must climb seven steps corresponding to the seven sacred planets, and in Judaism, the seventh Heaven is called the House of the Throne of Glory, guarded by the seven archangels.
Furthermore, even Japanese mythology speaks of the Seven Gods of Fortune.
7 in Everything
If you haven’t been paying attention to the things surrounding you until now, you surely will from here on.
There are 7 wonders of the Middle Ages, 7 wonders of the ancient world, 7 natural wonders, and the sky consists of 7 components. There are 7 colors in a rainbow, 7 musical notes, 7 seas, and 7 continents. The Bible describes the 7 days of the week, the 7 sins, and the 7 virtues of man.
Snow White ran off to live with 7 dwarfs, there were 7 brides for seven brothers, Shakespeare described the 7 ages of man, and when Ian Fleming was looking for a code for James Bond, he didn’t go for 006 or 008. Only 007 had the right ring to it.
Also, according to a study, if you ask a group of people to choose a number between 1 to 10, most of them will choose the number 7.
Researchers have also discovered that our mind can only retain up to 7 items at once. A larger group of elements must be split into smaller groups to be remembered.
777 in Slot Machines

Whether we know the significance of this number or not, it seems to be deeply ingrained in our DNA, and we almost always choose 7, whether consciously or not.
For all these reasons, it is also the luckiest symbol in slot games that offers the highest win.
Who doesn’t dream of having their favorite slot machine fill the screen with only the number 7?