Things can’t break if they do not change.
Mostly. Changing constantly is the hardware beneath.
I know things better if they have not changed.
Consider the expression,
(= (map f (reverse list)) (reverse (map f list)))
When is the expression true? As you think about it, you’ll realize that, of course, the two operands are always equal, thus the expression is always true. However, a hidden assumption was made – what is f? In the first operand, f is applied to the reverse list. In the second, f is applied to the list directly. These operands may not be equal if f is impure. That condition requires substantially more mental effort to understand this seemingly trivial expression.