The number 7 is seen as lucky because it appears often in slot machines, like...

https://quillhavenx.com/s/idSeoaJofGbZP_5X_hzAF

The number 7 is seen as lucky because it appears often in slot machines, like the classic 777 jackpot combo. It also connects to everyday cycles, like the seven-day week, giving it a sense of completeness