def distance_one(possible, word):
    """Checks if the number of characters changed between two words is one.
    Args:
        possible: str, possibly the next word
        word: str, real path word to test against
    Returns:
        bool, True if one letter distance
    """
    difference = 0
    for i, _ in enumerate(possible):
        if difference > 1:
            return False
        if possible[i] != word[i]:
            difference += 1
    return difference == 1