have docs explain why we import guard (#80569)

Co-authored-by: Matt Clay <matt@mystile.com>
Co-authored-by: Don Naro <dnaro@redhat.com>

docs/docsite/rst/dev_guide/testing/sanity/import.rst

@@ -10,6 +10,17 @@ This enables support for sanity tests such as :ref:`testing_validate-modules` an
 Handling import errors
 ----------------------
 
+Ansible executes across many hosts and can use multiple Python interpreters at the same time, which may even have different versions.
+To ensure users get an actionable and easy to understand error we try to ensure any non-core imports in modules/plugins are guarded to avoid a traceback,
+which most users won't be able to understand, much less use to solve the issue.
+
+Another reason Ansible does this is to import the code for inspection. This allows Ansible to easily test, document, configure, etc based on the code without having to install
+any and all requirements everywhere, especially when that is not the context in which you execute the code.
+
+The code below shows examples of how to avoid errors on import and then use the provided ``missing_required_lib`` to ensure the user knows which LIBRARY is missing,
+on which HOST it is missing and the specific INTERPRETER that requires it.
+
+
 In modules
 ^^^^^^^^^^
 
@@ -34,7 +45,7 @@ Instead of using ``import another_library``:
 
    The ``missing_required_lib`` import above will be used below.
 
-Then in the module code:
+Then in the module code, normally inside the ``main`` method:
 
 .. code-block:: python
 
@@ -59,7 +70,7 @@ Instead of using ``import another_library``:
    else:
        ANOTHER_LIBRARY_IMPORT_ERROR = None
 
-Then in the plugin code, for example in ``__init__`` of the plugin:
+Then in the plugin code, for example in the ``run`` method of the plugin (some plugins don't have a ``run`` method and will require it in the ``__init__`` method instead):
 
 .. code-block:: python