Is there anything more frightening than showing up (really showing up) in the place where you are unknown and alone?
All our warning systems are on high alert. From an evolutionary perspective, strangers represent danger. They are not only a direct threat, but carry the risk of rejection and all the insecurity that comes with it.
Add insecurity about your fluency with the language and customs. Know without a doubt that everyone is watching you all the time to see what you'll do since foreigners are so relatively rare. Welcome to Japan.