If 99 out of 100 people are vaccinated, the remaining person should be fine. "Should be" is the key phrase here—there are no guarantees in life—but while vaccinated people can still spread the virus, they're still much less likely to do so.

It's all a probability game. Add to this that the sole unvaccinated person is the one most at risk in any given setting, and I'm really fine letting them make their own choices.