What is the word for something where no matter how many times we repeat an action, it has no bearing on the outcome?
e.g. pressing the 'close doors' button on an elevator repeatedly doesn't make the doors close faster.
e.g. repeatedly clicking the mouse when your computer freezes doesn't help it unfreeze.
Example sentence:
"Repeatedly pressing the 'close doors' button in an elevator is a [insert word here] action"