I mean vaccines aren’t always 100%. If you’ve been vaccinated you’ll have a much stronger immune response, but it is still possible to get measles if you’ve been vaccinated. 2 doses of the MMR vaccine is on average 97% effective in preventing measles infection (per Mayo Clinic https://www.mayoclinic.org/diseases-conditions/measles/expert-answers/getting-measles-after-vaccination/faq-20125397).
The bigger issue (like with Covid shots, flu shots, and everything else) is that there are elderly & immunocompromised folks who can’t get vaccines. Their immune systems aren’t strong enough to handle the small dose in the innoculation. So the only way those people are protected is through herd immunity, relying on the rest of us to protect ourselves and our community.
When I got mine in they gave me local anesthesia, and it was still the most painful experience of my life. Turns out rummaging around in your innards produces a type of pain unlike anything I’ve ever felt. I truly can’t imagine how awful it must be without any anesthesia.