Some Chinese soldiers called it a “painful, little war.” Vietnamese troops avoided battle and instead harassed PLA forces. Some Chinese officers described it as a “ghost war,” since the enemy troops were almost invisible, or a “shadow war,” since it seemed they were fighting against their own shadows. The Vietnamese troops employed the same tactics, made the same moves, and used the same weapons as the Chinese. They knew exactly what the Chinese were trying to do. They exploited almost every problem and weakness the Chinese had. The Chinese troops had to fight their own problems first before they could fight the Vietnamese. Deng’s border war taught the PLA a hard lesson….
Hanoi believed, however, that the Vietnamese army had taught the Chinese army a lesson. One [People's Army of Vietnam] general said that China lost militarily and beat a hasty retreat: “After we defeated them we gave them the red carpet to leave Vietnam.” As Henry J. Kenny points out, “
Most Western writers agree that Vietnam had indeed outperformed the PLA on the battlefield, but say that with the seizure of Lang Son, the PLA was poised to move into the militarily more hospitable terrain of the Red River Delta, and thence to Hanoi.” Kenny, however, points out that Lang Son is less than twelve miles from the Chinese border but is twice that distance from the delta. Moreover, at least five PAVN divisions remained poised for a counterattack in the delta, and thirty thousand additional PAVN troops from Cambodia, along with several regiments from Laos, were moving to their support. Thus the PLA would have taken huge losses in any southward move toward Hanoi.
What the PLA Learned in Vietnam, 1979 | Far Outliers