Why was chain mail less effective against thrusting weapons?

Chain mail, a form of armour made of interwoven iron or steel rings, was highly effective at protecting the wearer against slashing strokes due to its flexibility.12

However, it was less effective against thrusting weapons because the concentrated force of a point could force the individual rings apart, even when those rings were secured with riveted closures. Because mail lacked the rigid, glancing surface provided by plate armour, it could not deflect or resist the piercing impact of a thrust as effectively as solid metal plates. This vulnerability, among other factors, eventually led to the development and adoption of plate armour, which offered superior protection against such focused attacks.21