I read many articles explain the Bitcoin POW, but every article seems copy form each other. they just indicate find a nonce start from 1, but I still confused why find a nonce number is so difficult? I know the hash value must lower than the target difficulty.
for example the Block #502500, the nonce is 3965324040, so this block hash value lower than the target when the nonce equal 3965324040.
if I start from 1 increasing the nonce to 3965324040, that is mean computer doing the SHA256 3965324040 times, but almost every mining pool already reached PHash/s, so they just need less 1 second to find the nonce?
after 2016 second would go to next difficulty? because they just took 1 second to find a nonce.
did I miss something there?