In my studies I learned how to think in an abstract way, without considering the whole details.
Visually the n-diagonal matrix was something familiar for me, it was the fascinating pattern, that reminded me of the windings of a screw or a spiral fusilli pasta. You can see how a full diagonal matrix is structured, it is also known as Toeplitz Matrix. As you can see it's a complex n-dimensional matrix, but think simple.
Substitute the variables into numeric values (for example a 4x7 Matrix), well the readability is much more better.