How can we say TCP is a reliable protocol?

If IP is going to carry the TCP packet, how can we say TCP is a reliable protocol?

The reason that Transmission Control Protocol (TCP) is considered 'reliable' is that the protocol itself checks to see if everything that was transmitted was delivered at the receiving end (it may not have been due to packet loss). TCP allows for the retransmission of lost packets, thereby making sure that all data transmitted is (eventually) received.

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