800-675, why do we borrow?

When doing vertical subtraction, 800 - 675 will turn out like this:

800

- 675

You should know that we start on the right and then end on the left.

So, we do 0 - 5, 0 - 7, then 8 - 6, right?

No. We have to borrow because you can't have a negative number when doing each number individually, only until the end. In this case, there won't be any negative numbers.

You can't do 0 - 5 or 0 - 7, so you have to borrow, changing the number to the left of it one lower (unless it's 0, so then you must borrow the the next number after that).

The reason why we borrow is because you cant subtract 0 from 5