Here's why:
* "Borrón" refers to an erasure or a mistake.
* "Cuenta nueva" means "new account".
The idiom literally translates to "erase and a new account". This signifies starting over, forgetting past mistakes and beginning anew.
Here are some other English expressions that convey the same meaning:
* To start fresh
* To draw a line under the past
* To turn over a new leaf
* To forget the past and move on
All of these expressions emphasize the idea of leaving behind past mistakes and beginning a new chapter.