Velcro and Sticky Notes! We knew how to fasten things, but before then we couldn’t fasten things in a half-assed fashion. As Laozi says in the Daodejing [Ch. 40,] “Returning is the movement of Tao; yielding is the way of Tao.” So, to be able to stick and unstick at will is the highest virtue under heaven.
[NOTE: Technically, research indicates both inventions predate me, but I don’t believe ether became popular for household consumer use until my lifetime.]
Tiger Riding for Beginners 