One of the major difference between a man and a computer is that machines have solid memory while ours is not that perfect. So the possibility of losing your passwords is more of a side-effect of being a human rather than anything else.

You can’t do anything about your human existence but help is at hand in case you have lost/forgotten your Mac password. There is an application in Mac OS X called Keychain Access which stores all kinds of passwords such as Wi Fi network, websites, mail, ftp etc.

For example if you have a bookmarked a site in Transmit FTP application with a password stored in the same and you want to retrieve it you can go to Keychain Access search for the name of the server you are interested in.

Now you may select the right key and get info with Apple(Cmd)-I. Now you will need to click the Show password switch which will prompt you for your admin password. Once you typed it in, the password for that specific key will now be visible.