This is very common in Elm but it blew my mind after years of programming in Python. In Python it is very easy to raise an IndexError by getting an element from a list by index that doesn't exist. eg.

    # python
    names = []

    names[0]  # <- raises IndexError

In Elm you are forced to always consider this possibility.

    # Elm
    names = []

    case List.head names of
        Just name ->
            name
        Nothing ->
            "empty"