I just quoted the source to avoid any lame rebutals but I don't think you a moron you just trusted the OP and he made crap up and you got stung.
a) if you went to the post office they wouldn't allow you to track first class stamp
b) if you used the website you can add tracking to first class letter
c) if you use software like stamps.com there is no option to add tracking to frirst class letter
d) nowhere anywhere on USPS website does it say you can add tracking to first class letter.
The truth is you probably never would have tried sticking a random tracking label on a first class letter expecting it to be free had the OP not mislead you.