why does append function affect other list?

Question

—-LISTS—-
list1=[1,2,3,4]
list2=list1
list1.append(5)
print(list2)

Result:[1,2,3,4,5]

—-VARIABLES—-
a=2
b=a
a+=1
print(b)

Result:2

Answer 1

the statement list2 = list1 assigns the variable list2 to the reference of list2(meaning list2 points to list1) so if list1 changes list2 will similarly change since it is actually a reference to list1 and not a new list

Answer 2

I’ve tried
list1=[1,2,3,4]
list2=[1,2,3,4] #1
list1.append(5)
print(list2)

But it returns [1,2,3,4]
On #1 what is the difference when i write list2=list1 ???