Why does the ICMP Echo Request packet not loop forever in the network?

What will be an ideal response?

traceroute command sets TTL maximum value for ICMP Request. Each router decrements the TTL field in the IP header by one. A router will not deliver this packet if Time to Live has exceeded the limit. Therefore, it will be dropped whenever TTL values become 0. Our loop involved 3 routers (Router2, Router3, Router4), so the TTL field of the packet is reduced by 3 for each circulation around the loop, as a result the TTL field was reduced to 0 after >21 circulations, and the packet was then discarded.