Object mutation [duplicate]

Why does this code error:

const obj = {
  one: 1,
  two: 2
}

obj = {
  one: 11,
  two: 22
}

But this code works:

const obj = {
  one: 1,
  two: 2
}

obj.one = 33
console.log(obj);

What does the following sentence mean?

though a const binding to an object can itself not be changed and will continue to point at the same object, the contents of that object might change.

Source