Complex sentence: Some languages, like Objective-C, allow you to assign to the this pointer, although this is generally discouraged, and can mislead, because it it does not modify the original object, only where it lives, and can end with undefined behavior.
Split into simpler sentences: Some languages, such as Objective-C, do allow assignment to the this pointer, although this is generally discouraged. So doing can be very misleading, because the assignment does not modify the original object, only where it lives, and can end with undefined behavior.