They mean stuff like https://en.wikipedia.org/wiki/Anencephaly https://en.wikipedia.org/wiki/Anencephaly. The brain is indeed incredibly resilient - some kids

They mean stuff like https://en.wikipedia.org/wiki/Anencephaly https://en.wikipedia.org/wiki/Anencephaly. The brain is indeed incredibly resilient - some kids with serious epilepsy get an entire hemisphere taken out - but which 5% you're left with matters enormously.