Another point of view

It's hard to explain to many people exactly how strong a 128-bit cryptographic key is. This is probably due to the difference between the numbers 128 and 2¹²⁸. They certainly sound very similar, but while 128 isn't too big, 2¹²⁸ is mind-bogglingly huge. And because 2¹²⁸ is so big, it can be hard to explain to people exactly how strong a 128-bit key is. Here's a new approach that might work:

The chances of guessing a 128-bit key are the same as your chances of plugging in a USB cable the right way 128 times in a row. How often does that happen?