It's more that "latent" typing (types do not appear in source code) and "structural" typing (types are determined by their structures, not by their names) are very important. Haskell and Ocaml fit both criteria, despite being strongly statically typed.
The reason for both is that you don't know the data types you'll be using when you start programming. It's very common to switch from a string to a hash to a structured record to an ADT, and if you have to change type declarations in every place that datum is passed to, you'll be spending most of your time changing type declarations.
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It's more that "latent" typing (types do not appear in source code) and "structural" typing (types are determined by their structures, not by their names) are very important. Haskell and Ocaml fit both criteria, despite being strongly statically typed.
The reason for both is that you don't know the data types you'll be using when you start programming. It's very common to switch from a string to a hash to a structured record to an ADT, and if you have to change type declarations in every place that datum is passed to, you'll be spending most of your time changing type declarations.