Every time you asked that friend where he was, he invariably said, "I am in my home in Moscow, Russia."
This friend has never been to Russia. No matter where he goes, the answer is always the same. He could be in the middle of the Arizona desert and insist he was at home in Moscow. When asked where his house was, he might say, "I have a really big backyard."
On every other matter under the sun, you would have a perfectly reasonable conversation. Just as long as you didn't ask him where he was. It's just on this one quirky issue that this person has an unshakable -- but obviously false -- belief.
(There are cases of people with particular brain damage who do, in fact, have these sorts of convictions. So this is not purely a hypothetical case.)
What would you say if that person ran for Mayor of your town? Would you recommend him?