Relation in one table

I have table books (model Book) with columns: id, group_key, content. And I have 3 rows in this table:

1 | 1 | content1
2 | 1 | content2
3 | 1 | content3;

In model I have relation

public function allGroupItems()
{
    return $this->hasMany(self::class, 'group_key');
}

I get first item in table and try to use relation allGroupItems to get all rows in table with the same group_key as in first item.

$book = Book::find(1);
dd($book->allGroupItems); // 3 rows

And I succeed. I'm getting 3 rows as expected. But if I try to do the same with second or third row, I'v got empty array as result:

$book = Book::find(2);
dd($book->allGroupItems); // empty array

I expect to get the same 3 rows. I don't understand why I am getting an empty array. What's wrong?

Laravel 9.52.7, php 8.2.1

public function allGroupItems(): HasMany
{
    return $this->hasMany(self::class, 'group_key', 'group_key');
}