From what I gathered so far, Tracert works by sending 3 ICMP echo messages. Starting with a TTL value of 1. For each router the packet encounters, the TTL value will be decremented. For the 1st router, 1-1 = 0, so an ICMP "time exceeded" message will be sent back to the sender machine. Next, the TTL value will be incremented to 2 by the sender machine and the cycle repeats for the 2nd router (2-->1-->0) and so on.
Please correct me if my undestanding is flawed.
I am curious as to why the ICMP "time exceeded" message isn't displayed by Tracert in Command Prompt since it is in fact an error message ? The cycle simply proceeds on.