What will happen if you forget to include "self" in a method definition?

In Python, when defining an instance method within a class, the first parameter must always be a reference to the instance of the class, conventionally named "self." This parameter allows the method to access attributes and other methods on the instance. If "self" is omitted during a method definition, Python will not recognize where to find the instance related to the method call.

As a result, when you attempt to call such a method on an instance, Python will raise a TypeError indicating that a required positional argument is missing. This error arises because the method definition lacks the necessary reference to the instance context, which is essential for accessing instance variables and other methods correctly. Therefore, without "self," the interpreter cannot execute the method as it does not know which instance to operate on.

The concept of including "self" as the first parameter is crucial for instance methods to function as intended in object-oriented programming and to maintain the correct association between the method and its instance.