The horrendous losses inflicted on Viet Cong units struck into the heart of the irreplaceable infrastructure that had been built up for over a decade. MACV estimated that 181,149 Viet Cong and North Vietnamese troops had been killed during 1968. From this point forward, Hanoi was forced to fill one-third of the Viet Cong's ranks with North Vietnamese regulars. However, this change had little effect on the war, since North Vietnam had little difficulty making up the casualties inflicted by the offensive. Some Western historians have come to believe that one insidious ulterior motive for the campaign was the elimination of competing southern members of the Party, thereby allowing the northerners more control once the war was won.

The Viet Cong lost, and lost big, in just about every battle. But after months if not years of US leaders saying that they were winning the war, the offensive was a major shock to the US public.

Weird that this happened (barely) in my lifetime and it is treated as ancient history on Wikipedia.