Appending to one list in a list of lists affects all other lists if they reference the same object. In Python, lists are mutable, and when you create a list of lists using a shared reference, all sublists point to the same memory location. Modifying one sublist changes all of them because they are not independent copies.
Example:
lists = [[1]] * 3 # All sublists share the same reference
lists[0].append(2) # Affects all sublists
print(lists) # Output: [[1, 2], [1, 2], [1, 2]]
To avoid this, use copy() or list comprehensions to create independent sublists.