Think about your keychain. It probably holds the necessities: car keys, home keys, work keys, miscellaneous keychains you bought on your previous vacations. Now, imagine you have a keychain full of these keys that all look the same, but each only opens a specific door.
Sounds kind of like your list of passwords, right? But what happens when you have all of these keys, and you need to get into your house? In either situation it can be easy to forget which key, or password, goes to what door or web