There is am old German saying: "Gegen Dummheit kämpfen Götter selbst vergebens". But I don't believe in this. "Stupidity" is mostly caused by trauma, often from past lives (there sometimes are rare genetic reason for it - mutation in the dopamine receptor -, but this is the exception). De-traumatize people and teach them having fun in learning (which is abslolutely possible) - you will be surprised about the results.