Inheritance in Javascript MDN Question

learning

#1

On this link below:
https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Objects/Inheritance#Setting_Teacher()'s_prototype_and_constructor_reference

I don’t quite understand what point 2 and point 3 meant. Why do we need to write Teacher.prototype.constructor = Teacher; and what “problem” can it cause if we don’t?