Parents who do their best and have it turn out badly do not need to blame themselves. It may be the child's nature that overcomes the best possible nuturing. Also of course there are many other factors besides the family that complicate the child's upbringing.
I raised a number of adopted children (my wife and I were unable to conceive), and some of them had had really rough infancies (because of war). Even though we are a literate family with lots of books and so on around, and in spite of a lot of effort and special schools, two of our children remained illiterate -- and Vietnamese is an easier language to learn to read than English. They are both happy and productive adults, but it is still something hard to accept or even understand.
You must mean Locke's tabla rosa, I think he really pushed that environment triggered existing potential.
I tutor kids who have learning disabilities and the common thread is their early environment's were awful.