Honestly the best way to learn how a runtime works is to learn how to debug it at the lowest levels. Read every single article here: Tess Ferrandez on MSDN[^]. Read if from start to end (well, actually end to start) and you should have really good in-depth knowledge (granted, reading and digesting that whole blog will probably take a few months). Real-world experience/stories sticks a lot better than raw theory (at least in my experience).
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chinese Proverb]
Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore, Dream. Discover.