The first three steps of the Mastery Technique are about action: learning, applying, practicing. This fourth step is about mindset: are you striving towards mastery when you do the first three steps, or are you just going through the motions?
Striving for Mastery is what takes place in your mind as you practice the knowledge, skills, and rules from the first three steps. How do you react when you get a question or problem wrong? Do you shrug it off with a “whatever” or do you take a moment to question yourself? Why did you get it wrong? What made you choose the answer which turned out to be incorrect? If you try to learn from these mistakes, even if they’re very tiny, like getting “3×8 = 24” incorrect, you’ll strengthen the neural pathways that reinforce the correct answer and the newfound skills.
It needs to be stressed that the phrase isn’t “strive for average.” It’s Strive for Mastery! You truly want to master the knowledge and skills at hand, because (especially with math) these provide the foundation for the next step in your education. You want to learn the basics to the point of automaticity, so that you don’t even need to think about them as you pursue more difficult knowledge and skills.