How does one formulate a backtracking algorithm

Question

I am new to learning algorithms. I was reading backtracking algorithm for generating all strings for n bits. If I dry run the program I know the program is giving right result. But I didn't understood the logic can anybody please explain? What I mean is what will be be the thought process to arrive at this solution

void binary(int n)
{
    if(n < 1)
        printf("%s\n",A);    // Assume A is a global variable
    else
    {
        A[n-1] = '0';
        binary(n-1);
        A[n-1] = '1';
        binary(n-1);
    }
}