reduce passwords I must type How can I reconfigure my MBP to require me to type username &amp; password only once, going all the way from shut down to functional?

I think industry-standard naming is confusing in this area: the term "login" is ambiguous, sometimes meaning "the username," sometimes meaning "the username and password," and sometimes meaning "the act of entering username and password into the system." I will try to use these terms consistently:


username means the string which identifies the user
password means the string which proves the human at the keyboard is the claimed user
credentials means the pair of strings (username, password)
login means the act of entering credentials


I have seen various similar MBPs exhibit different behavior in this regard: some do it as desired (one login); some require two logins; some require three. I have learned, through search and experiment, that the "3" case can be improved to "2" by ensuring that the account password matches that of the keychain item which is (also) named "login."  So far, so good.

I tried essentially the same trick to eliminate the second login: I made the FileVault 2 credentials match the account credentials. On one computer, this worked: I can now log in to this computer via a single typing of credentials. But on another computer, this did not work: all credentials are the same, yet it takes two logins to get in.

I believe OS X normally keeps all these credentials in sync, so the fact that they were out of sync to begin with may be significant. Unfortunately, in considering the computer that works as I want, it is impractical to recover the history of how it got there, due to limited expertise of the owner.
This is pretty simple.

In System Preferences 


go to the Users &amp; Groups Preference Pane
click on Login Options
click to unlock (bottom left) if needed and authenticate
verify Automatic Log in is on the user you wish to use
go to the Security &amp; Privacy preference Pane
enable your user for FileVault
reboot


You will select your user from the picker and then enter your password one time and then you should be logged in. If you have a bad user, you can add a new admin user, let it unlock FileVault - remove the problematic user but do not delete the home folder. Then rename the /Users/whatever (deleted) to be the short name you wish and re-create the user. Be sure the keychain is unlocked when that new user password is set up when you log in. Authenticate the new user to FileVault and remove the "new admin" user from above.