diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md
index 672faad6f162ba615e4c8a7dd4e4d8f7e9e2a2a9..e076f10ece4bd9410f9a78f156f8f07935402ce9 100644
--- a/guides/source/association_basics.md
+++ b/guides/source/association_basics.md
@@ -2350,6 +2350,17 @@ end
 
 If a `before_add` callback throws an exception, the object does not get added to the collection. Similarly, if a `before_remove` callback throws an exception, the object does not get removed from the collection.
 
+NOTE: These callbacks are called only when the associated objects are added or removed through the association collection:
+
+```ruby
+# Triggers `before_add` callback
+author.books << book    
+author.books = [book, book2]
+
+# Does not trigger the `before_add` callback
+book.update(author_id: 1) 
+```
+
 ### Association Extensions
 
 You're not limited to the functionality that Rails automatically builds into association proxy objects. You can also extend these objects through anonymous modules, adding new finders, creators, or other methods. For example: