Like, for example, if you reduce a 1 in 10 chance of something to a 1 in 1000 chance, that doesn't mean it definitely won't happen, it means it's substantially less likely to happen. And if you apply that to a large group of people, it'll happen to fewer people. So in a group of 1000 people, in that example, something that would have happened to around 100 of them would still happen, but only happen to around 1 of them.
And we know that the vaccine is effective in that regard, reducing risk, from looking at what happens in large groups of people who were vaccinated compared to large groups of people who weren't.
So going, "but it happened to this one guy I know," means literally nothing to this conversation.