When I was a child, it used to drive my mother nuts that I would use the accusative case in coordination. For example, I’d say things like (1)

(1) John and me are going to play in the yard.

My mom would scream “John and I!!!”

She didn’t explain to me about nominative and accusative case and how pronouns should behave (not to mention the fact that she was trying to get me to learn a completely prescriptive rule). So I thought and thought about it and finally trained myself to always use “I” when I used “and.” So I ended up with not only sentences like (2) but also like (3).

(2) John and I are going to play in the yard.

(3) *Do you want to play with John and I?

Granted, in this case we are talking about prescriptive rules and Tom’s lecture was about innate rules of grammar, but it still seems to be the case that if we think about correcting our langauge we rarely get it right –and it is something we have to memorize, whereas language acquisition appears to be entirely effortless.