I followed this advice, I used document.querySelectorAll() with a .slice() hack instead of jquery and similar methods. As I needed more and more functions I kept adding them, and now I have a beautiful jquery alternative [1].
It has helped me a lot to learn core Javascript concepts, testing my code and hating Internet Explorer even more. I wouldn't change everything that I have learned for anything. So try it, create your own small library, you'll learn a lot.
So as time goes by, you ended up creating a jquery alternative. Now imagine you work on a large team and everybody ends up creating their own frameworks...
That would be awesome since then everyone would learn A LOT about javascript. But to work together with other people, one of the first things to decide is the technology; and if you create something from scratch as a team, you do it together, not each one their own.
It has helped me a lot to learn core Javascript concepts, testing my code and hating Internet Explorer even more. I wouldn't change everything that I have learned for anything. So try it, create your own small library, you'll learn a lot.
[1] http://umbrellajs.com/