So imagine you are 10 years old, RIOT is your parents and it's your birthday. Your parents let you make a birthday party but they are RIOT.
RIOT says: You know, son, you celebrate your birthday every year and we want it to feel for you really special, so we let you invite only five friends out of 150 and they will be random, we don't care if you hate them or love them, you will celebrate your birthday with them or you not at all and wait next year (5mins)
YOU: but mom! What about my best friend?! What if he won't be picked as that random friend?
RIOT: don't worry you can reroll one of your friend and chances from 1/150 becomes 1/75. So you'll have to celebrate 75 birthdays to statistically get your best friend in your birthday.
Wait... I have a perfect idea, lets make that all of your friends have to have blue eyes and if they don't, they can't participate. Oh your best friend has green eyes? So sad
(If someone didn't get it, it was related to ARURF)