PLA lost both wars, Korean and Vietnam.

Just think why you retreated while your goals were not accomplished. 

In Korean War, PLA could not hold on anymore because US strategy was changed and PLA did not have enough food, clothes, and ammunitions.  Soviet Union wanted the war to stop so PLA stopped.  For US, if it wanted to beat PLA, it could but it was worrying about Soviet Union's atomic bombs.  In fact, all communist officials were packing in Shanghai, ready to go back to Shangxi to fight guerilla war.

In Vietnam War, still remembered the snail pace of the war.  When LianShan was finally reached after so many days, I was stunned when PLA retreated.  That's it?  What was the point of attacking Vietnam? Taught them a lesson? With so many lives lost?