With most things, it is difficult to achieve mastery without a constant commitment to learning new things and a steady application practicing that learning.  That's why an expert is someone who knows more and more about less and less.  When it comes to digital marketing, pick an area or two to really know, and then partner with or rely upon professionals for everything else.  Always ask good questions.  Always ask your service provider to be able to demonstrate a return on investment or a progression in agreed upon metrics.  But realistically speaking, in the long run, professionals work with professionals.