To acquaintances, I might be a Pavel; to close friends, I might be Pasha. To my mom, I'm Pavlik. In a business or other more formal setting, I would be Pavel Dmitrievich.
I think it's a common complaint when reading Russian novels, non-Russians get confused about who's who because of these types of shifts. And it totally makes sense; at least my various nicknames start with the same letter, but many Russian "short" names don't particularly resemble the full name. Who would expect Aleksandr to be Sasha, if you didn't grow up in the culture?