The vaccine makes you less likely to get it.
Having the Chicken Pox as a child doesn’t mean you won’t get Shingles. It just makes it less likely.
Actually, having chicken pox as a child is how you get shingles as an adult. Once you have chicken pox, the virus remains in your nerves forever. The shingles vaccine is supposed to boost your immune system to decrease the chance that the virus can reactivate.
Having chicken pox was no fun. Neither was shingles.