if they used static types it would be 100%

statically typed languages are to be seen as safer than their dynamic counterparts. While this might be true when comparing with many dynamic languages, Erlang begs to differ and certainly has a track record to prove it. The best example is the often reported nine nines (99.9999999%) of availability offered on the Ericsson AXD 301 ATM switches, consisting of over 1 million lines of Erlang code

Statically typed systems can't grow or change.
Think about the classic OO examples like Person. A dynamically typed Person can learn how to play the piano. If it's statically typed, that's impossible.
This is the same reason why pure functional programming sucks.