That’s easy – the rubber. No, not that. Though that should probably be quite high on the list too. No, I mean the ‘eraser’, to use its more transatlantic name. Anything that enables us to rub out our mistakes and correct them; to go back and put things right.
True, it’s not really a single great innovation I’m plumping for – more a category, encompassing many diverse innovations, from chalk and slate to the delete button on your computer keyboard to the bulldozer.
But it’s an all-important category. As the old saying goes, if you’re not making mistakes you’re not trying hard enough. And with the ability to correct our mistakes comes the confidence to risk failure, to experiment with abandon and to generally give the boundaries enough of a kicking to advance them on a bit.
If only everything came with such a capability for ‘infinite undo’.
That’s my number one choice. Though I’d probably also give an honourable mention to the invention of the alphabet and writing, which facilitated the first long-distance communications and the widespread dissemination of knowledge - not to mention bringing enjoyment to many millions of readers and giving scribblers like me something to do all day.
Paul Parsons is the Editor of BBC Focus magazine and managing editor of BBC Sky at Night magazine.