This is the opposite of my point of view. I think it’s a great example because the whole point is that, while most people’s everyday experience of a bank accoun

This is the opposite of my point of view. I think it’s a great example because the whole point is that, while most people’s everyday experience of a bank account is as a single mutable value, the reality is far more complicated and subtle. Teaching is all about using simplified examples to convey intuition, and “you might think it’s easy to keep a single number up to date, but moving money between two accounts is fraught with danger” is a perfect demonstration.