Why does the summation of these indicator variables start from i<j?

Question

I'm currently reading through the eighth edition of A First Course in PROBABILITY, by Sheldon Ross. The section I'm reading is "Momens of the number of events that occur", and I understand everything below except for in the case of the summation of $I_iI_j$, why are they starting from $i<j$?

Answer 1

If the summation were over all $i\ne j$, then every pair would be counted twice.