Well, *puts on Neil DeGrasse Tyson glasses... a 5% chance isn't the same as 1 out of 20.
When you do a raid, you have a 95% probability of not getting a shiny. If you want to calculate the probability you won't get a shiny in two raid, you'd multiple 95% by 95% and get 90.25%. So, rather than a 10% probability of finding a shiny, it'd be 9.75%. With 3 raids, 95% x 95% x 95% = 85.7375%, a 14.25ish% probability. With 10 raids, 59.87% no shiny. With 20 raids, 35.84% no shiny. So, with 20 raids, the probability of getting one is 64ish%. Pretty high, but not 100%.
With 30 raids, 21.46% no shiny. With 40 raids, 12.85% no shiny. After 40 raids, there's a probability that about 1 out of 10 people would not have gotten a shiny. Anyway, you can keep going, but it'll never be 100%. Of course, that's all just probability. Every time, it's 5%.
Pokemon Go Luck is weird anyway. I mean, how many Charge TMs have we wasted on a 50% chance. It's like Casino luck.
Pokémon Go | Era Edition | Upgrade 2.0 Catch Pokémon in the Real World with Pokémon GO! Explore your town to gather up items from Pokestops & Gyms. Collect Pokemon and battle your way into gyms. Check out the local Raid scenes to meet up with others. Download from: Apple App Store | Android...