That depends on who you are, really! Often, business owners, marketers, or entrepreneurs can do certain parts of digital marketing, but not all of it. An agency can be helpful in terms of devising a coherent strategy, allowing you to make use of experts to get better results, and figuring out where to best spend your money. But you don’t have to outsource all (or any) of it, especially if you’re willing to learn and already have a knack for, say, writing social media captions or interpreting analytics data.