In this story on why it's better to travel alone, the fourth reason is my favorite: deep immersion.
You simply are not going to see or notice as much if you're walking with a friend or partner, while in Paris or Tokyo or anywhere else, gabbing with each other about what you just saw or where your next meal will be or something you remembered about your lives at home. You've stopped absorbing what's around you at that moment.
That hit home for me while I was in Paris on my own for a month-long French immersion course the summer before grad school.
Although the rule in the apartment I was staying in was French only, I had an English-language novel with me. I realized early on that reading in English was pulling me away from a full immersion in French language.
It demonstrated my brain's inability to focus as well on learning French when I mixed in some English. I put down that book for the summer. Soon after, I awoke from a dream with a French phrase in my mind first thing. Immersion was working!