Why do we blink very quickly?

Why and how fast we blink

Blinking is a protective reflex that lasts only a three to four-tenth of a second, but that's all the time needed to clear away dust particles and moisten the eyeball. The frequency of blinking increases when talking, nervous, in pain, or when exposed to very bright light. 

Wondering why you don't notice the darkness of the world every three tenth of seconds? It's because the act of blinking suppresses activity in several areas of brain responsible for detecting environmental changes, that's why we experience the world as continuous.