Why do you need deep comparison?

reference: https://dmitripavlutin.com/how-to-compare-objects-in-javascript/

Following to the reference, deep comparison is:

The deep equality is similar to the shallow equality, but with one difference. During the shallow check, if the compared properties are objects, a recursive shallow equality check is performed on these nested objects.

const objA = {
  propA: 123
  propB: 'a'
  propObj1: { // assume reference: 1234
     propObj1: 'abc'
  }
}

const objB = {
  propA: 123
  propB: 'a'
  propObj1: { // assume reference: 1234
     propObj1: 'abc'
  }
}

Is it possible for objA and objB to be equal in shallow comparison but not in deep comparison?

Because their propObj1 have the same reference, change to objA.propObj1 will be also reflected to objB.propObj1 which means they will also be equal in deep comparison. Can you give an example where it is true in shallow comparison but false in deep comparison?