There are several ways to have a limited ability to think:Born that way by genetics as with Down's Syndrome. Born that way by mother's bad habits as with fetal alcohol syndrome. Get hit in the head, traumatic brain injury, concussion. Stress of life. Substance abuse, prescription drugs that alter brain chemistryChemicals in ordinary objects like aspartame, lead, mercury, etc. Electro-magnetic wavesSelf-delusion, people get depressed, think too much, etc. My main purposes in writing this book are:To find all the conventional knowledge about mental challenges as I could and centralize it here. It is evident when a child is born with down syndrome or his or her performance seems slower than normal but everything else is someone's opinion as with autism spectrum disorders and learning disabilities. People who diagnose these so-called disorders have no specific test that can with certainty say they have this disorder therefore need this drug.