Let me preface this by saying that I think this is a great article. It has all the primers for what one would need to know to learn digital marketing.
With that said, I would love to write a follow up called "How to become PROFICIENT at digital marketing in 10 years". Digital marketing is a constantly evolving ever changing environment. Becoming proficient at anything takes much longer than 6 months. The day to day job of a digital marketing agency is all encompassing. One needs to be highly skilled in the latest lead generation platforms, marketing techniques, and under the hood optimizations that take much longer than 6 months to learn. I know people that have been focusing on simply FACEBOOK lead generation platform for 3 years and are just starting to become proficient enough at delivering solid ROI to justify their campaign management expenses.