A good word from Josh Kaufman in his book The Personal MBA:
One of the beautiful things about learning any subject is the fact that you don’t need to know everything — you only need to understand a few critically important concepts that provide most of the value. Once you have a solid scaffold of core principles to work from, building upon your knowledge and making progress becomes much easier.
Along with this, Kaufman quotes Ralph Waldo Emerson’s helpful point on methods and principles, which is good to keep in mind:
As to methods, there may be a million and then some, but principles are few. The man who grasps principles can successfully select his own methods. The man who tries methods, ignoring principles, is sure to have trouble.