I have trouble understanding why sometimes it occurs that during IP fragmentation certain fragments take different routes. I was following this the second example: https://www.gatevidyalay.com/ip-fragmentation-fragmentation-in-networking/
If the fragmentation is done by router-2 as I concluded it should, how does the second fragment take a detour over router-3 and network z with a different MTU? The provided explanation led me to believe that the fragments are returned to the source and repeatedly sent, but then how isn't the first fragment traveling directly and not taking a detour?
I am pretty new to networking and until now I was into backend programming while I graduated math so I am sorry in advance if I ask redundant stuff.