While Einstein was not a neuroscientist, he sure knew what he was talking about in regards to the human capacity to achieve. He knew intuitively what we can now show with data—what it takes to function at your cognitive best. In essence: What doesn’t kill you makes you smarter.
Not so many years ago, I was told by a professor of mine that you didn’t have much control over your intelligence. It was genetic—determined at birth. He explained that efforts made to raise the intelligence of children (through programs like Head Start, for example) had limited success while they were in practice, and furthermore, once the "training" stopped, they went right back to their previously low cognitive levels. Indeed, the data did show that [pdf], and he (along with many other intelligence researchers) concluded that intelligence could not be improved—at least not to create a lasting change.