What is the difference.

[jarrod0987]

Having a problem I can't understand. I can print one global string but not another.

#Playfair ENDE

LETTERS = 'ABCDEFGHIKLMNOPQRSTUVWXYZ'
MESSAGE = '''Oh, I see you ate one too!'''

def main():
    print (LETTERS)
    print (MESSAGE)
    MESSAGE = '''Oh no I didn't'''
    print (MESSAGE)




if __name__ == '__main__':
    main()

When I run it I get :

Error:
ABCDEFGHIKLMNOPQRSTUVWXYZ
Traceback (most recent call last):
  File "C:\Users\jarrod0987\AppData\Local\Programs\Python\Python36-32\Stub.py", line 16, in <module>
    main()
  File "C:\Users\jarrod0987\AppData\Local\Programs\Python\Python36-32\Stub.py", line 8, in main
    print (MESSAGE)
UnboundLocalError: local variable 'MESSAGE' referenced before assignment

Why does LETTERS print but MESSAGE not print?