What’s wrong with my password?

Yesterday, I was attempting to log in to one of my desktop computers like I had for the last two years. Normally, I never have problems and today everything I tried failed to log in.  I started thinking of all my passwords for all my accounts and tried my others which failed.  The username was retyped just in case it was incorrect and I noticed the username was in capitals as it was typed.  I had accidentally engaged the Capital Lock mode  with the CapsLock key!  I depressed it and typed my username and password again and this time I logged into the computer’s operating system.  Remember, passwords are case-sensitive while usernames are usually not. This applies to Macs, Microsoft Windows and Linux computers.