By 1968, NVA morale was at it's lowest point ever. The plans for "Tet" 1968 was their last desperate attempt to achieve a success, in an effort to boost the NVA morale. When it was over, General Giap and the NVA viewed the Tet 1968 offensive as a failure, they were on their knees and had prepared to negotiate a surrender.
At that time, there were fewer than 10,000 U.S. casualties, the Vietnam War was about to end, as the NVA was prepared to accept their defeat. Then, they heard Walter Cronkite (former CBS News anchor and correspondent) on TV proclaiming the success of the Tet 1968 offensive by the communist NVA. They were completely and totally amazed at hearing that the US Embassy had been overrun. In reality, The NVA had not gained access to the Embassy--there were some VC who had been killed on the grassy lawn, but they hadn't gained access. Further reports indicated the riots and protesting on the streets of America.
According to Giap, these distorted reports were inspirational to the NVA. They changed their plans from a negotiated surrender and decided instead, they only needed to persevere for one more hour, day, week, month, eventually the protesters in American would help them to achieve a victory they knew they could not win on the battlefield. Remember, this decision was made at a time when the U.S. casualties were fewer than 10,000, at the end of 1967, beginning of 1968.
Vietnam War Stories: Tom Hayden, Jane Fonda, Hanoi Hannah. 1965.