I was pretty amazed when someone brought this up and a solution exists. The way I was taught is that if you lose your password you're done.

Just use GRUB to boot into single user mode / recovery mode.

(1) At grub boot screen (after restart)

(2) Select the kernel

(3) Press the 'e' key to edit the entry

(4) Select line starting with the word 'kernel' or 'linux'

(5) Append the letter 'S' (or word 'Single') to the end of the line

(5) Append 'init=/bin/sh' to that line also

(6) press cntrl-X

(7) mount the root filesystem if it isn't already done for you

(8) type 'passwd <enter>' to reset the root password 

(8) type 'passwd <user> <enter>' to reset user's password.