Certified mail rarely gets lost and usually arrives on time to the person that the certified mail is being sent too.
However just like all mail that can get lost sometimes certified mail can indeed get lost in the mail system as well but certified mail is less likely to get lost than regular mail is.
Mail that requires on time delivery and mail that wants to be sure to get delivered to a person will be sent certified so that the person or company knows that the person gets the mail.
Important documents are usually sent certified mail and sometimes restricted certified mail where the person listed on the mail address will have to sign for it and show ID so that it gets directly to the person the restricted certified mail is addressed too.
Whenever I've sent certified mail It's always showed up to the address it was supposed to and on time and never have I had certified mail get lost.
But it is indeed possible for certified mail or any other mail to get lost.