A major problem is that the electoral system is chaotic. In the sense of chaos theory: small deviations in input (votes) lead to large differences in the result

A major problem is that the electoral system is chaotic. In the sense of chaos theory: small deviations in input (votes) lead to large differences in the result (electoral college votes). The pollsters were off only be like 2-3% or so, and a bit the distribution. Also, it appears Trump Supporters were often too ashamed to be honest to pollsters.