Imagine for a moment that someone stole the key for your bicycle lock. But since it’s locked safely in your garage anyway, it’s no big deal, right?
Now imagine that, for convenience, you had previously rekeyed every other lock you have so you could use that bike lock key in all of them. Your front door, your car, your mailbox and your safe deposit box at the bank are only secure if you keep that one key safe. Now how would you feel if you lost it?
Of course, nobody would be so careless as to make one key fit every lock, right? Well, take a moment to consider how many dozens of online accounts you have. How many of them use the same password? Think about what would happen if just one of those sites was hacked, and someone got a hold of your login information.