Accidents do happen and stuff can genuinely get lost in the mail. But, I believe that most stuff that does not reach its destination is stolen rather than lost. Please don't get me wrong, I believe the most postal employees are good, hard working Americans, but there has to be a few bad seeds. Think about how many hands must touch each piece of mail, you only have to cross one bad seed in order to "lose" your stuff. I firmly believe that people who regularly handle the mail can sense if there is something of value in an envelope. It is the senders job to make it as difficult as possible to detect the contents. A chip in an envelope appears to be a silver dollar, it is just too tempting.

My rules for mailing chips are:
1) Always use a bubble mailer
2) Put the chip inside a holder, like a plastic 2x2 or a plastic page. This converts the round chip into a square item. It no longer appears to be a silver dollar.
3) Make sure the chip cannot move around inside the envelope. I then wrap the holder into a piece of paper with the details of the deal.
4) Seal the envelope so that it cannot be easily opened and resealed. I staple the envelope closed and then seal with packing tape.
5) Insure the item when its replacement would be too costly.