Packets can be lost because of the physical connection causing bits to flip from “1” to a “0” (or vice versa). A single bit error in a packet will cause the whole packet to be dropped by the first node receiving the packet.
The Transmission Control Protocol (TCP) is addressing the need for packet loss recovery using the Automatic Receive reQuest (ARQ) mechanism. ARQ requires the receiver to send acknowledge to the sender for each packet received. If the sender is not receiving acknowledge within a pre-defined time, it will retransmit the packet.