In some countries Sunday is considered the first day of the week, which is quite strange for me, as here it's Monday.

Do Americans, for example, feel like "a new week has started" on Sunday morning? For me Saturday and Sunday feel as one block, it's weird to imagine a separation in there.

But perhaps someone who grows up with that calendar feels like Saturday is end-of-the-week winding down, and Sunday is a start-of-the-fresh-week "warmup" day.

American and even I've never understood why Sunday is considered the first day on some calendars. It has always, in my experience, been considered a weekend day and you would think that the "weekend" is at the end of the week, and Monday has long been the default start of a work or school week.