I love the unknown most of the time because it offers the opportunity for learning and dreaming and provides a playground for the brain, especially the imagination. Some unknowns are annoying. Two unknown numbers called today and they didn't leave a message. I was sleeping. The last call woke me. This day time culture can be very annoying to my nocturnal circadian rhythm :)
The annoyance is unknown numbers with no messages. Those are typically sales calls and I block those numbers. One was from a telemarketer in Chicago searching for credit card numbers and is a reported scam according to this site: http://findwhocallsyou.com/7734579620 and another number is a fraud reported number according to this site http://findwhocallsyou.com/407-545-3497 ... much annoying. That is why I don't answer unknown numbers and if someone (legitimate) calls I might block them even if they are a friend. Most friends know they need to leave a message if they are calling from a number that is not in my phone and most friends do.
The National Do Not Call list https://www.donotcall.gov run by the government has helped a lot as I seldom get unsolicited calls. The criminals phishing for identity theft information are not going to abide by those rules, however, so I block. I just spent an hour looking up unknown numbers I received over the past year. Some got blocked as SPAM, some got blocked as "Unknown" and a few I left suspecting they were softball players who's numbers were never entered into my phone. Some of the blocks might be softball players or even friends calling from unknown numbers. Annoying, yes.