special relativity - Why do we restrict the maximal supercharge to 32?

Many supersymmetry textbook state that the maximal supersymmetry in any dimension has 32 hermitian supercharges. (Actually for lowest number of supersymmetry $N=1$ the highest dimension is $D=11$)

I want to know why the maximal supercharge is restricted as $32$.

Answer

Because you want the maximal spin particle allowed to be 2 (since there is no higher spin field theory interacting non trivially), thus in a supermultiplet starting with a particle with helicity $0$, say in $d=4$, the maximal number of susy you can apply is $8$, thus $N=8$ in $d=4$ is the maximal supersymmetry admitted, which means $32$ supercharges.