One of the reasons why moving to a totally new city is so tiring is that everything matters.
At both a conscious and unconscious level, you are constantly taking in everything – because you don’t know which pieces of information are significant and which aren’t. So, to give a trivial example, you note a post-box as important information, but if you discover another one closer to your house, you downgrade the importance of the first post-box: it becomes filed in your background memory, as opposed to your working memory.
Everything matters, until you are in a position to determine which things don’t matter. That means you don’t take anything for granted. And that comes with a real positive: with fresh, outsiders eyes, you see things that the indigenous population don’t see any more, things that will fade into the background until you don’t see them either. Such people ask questions that might be significant, that might lead to constructive change – and at the very least, lead to a greater understanding of the new-to-them context. But the downside is that it takes so much mental and emotional energy that it leaves you feeling physically tired – whether you find new environments mentally stimulating or draining.