If you have been blocked by another cellphone user and then try to send a message, in most instances you will see your message "delivered" or "sent", but not "received".
The exact terminology depends on what phone/messaging app you are using. For example, iMessenger uses the term "read" when an SMS has been opened.
What's even more confusing is that, a mobile phone user can actually turn off the "timestamp" updating you about whether they see your messages or not.
In this instance, all messages you send will go out as normal and do not return with a failed message, but the recipient will never receive a single SMS from you.