Why did China win the battle of Nansha in 1988, and so many islands were occupied by Vietnam?

Nansha Islands are easy to attack but difficult to defend, and Vietnam is much closer to those islands than China. The previous China navy was not strong enough to take care of it; China put forward the idea of "shelving disputes and developing together", but only China foolishly abides by it, and others don't care about you. We always focus on economic construction and the overall situation, allowing small Vietnamese to run amok and let him push his luck; It is necessary for China to teach those shameless small countries a lesson!