Why put a -1 in the range?


Hello, I'm a bit confused as to why we put a -1 when we're talking about a range, for example:
In Battleship 12 "Bad aim":

  if guess_col not in range(0, len(board) -1) or guess_row not in \
    range(0, len(board) -1):
        print "Oops, that's not even in the ocean."

I put those -1s there because one of the hints told me to. But what are they even doing?
Thanks in advance!


Hint: Array indexes begin from 0, continue upto length of board - 1.