Can a Good Writer Be Bad at Diagramming Sentences?

I still remember standing at the chalkboard in Mrs. Kopald's fourth grade class diagramming a sentence. I had no idea what I was writing or why. I drew a straight line and all these branches and just wrote stuff on them. I didn't know what I was really doing and still don't know a past participle from a gerund or direct object. 

I felt similarly about iambic pentameter  in high school which looked like this:

 ×  / ×   /   ×  /      /  ×    ×   / (×)
To be or not to be, | that is the question

These were the types of activities that turned me off from writing for so many years. Can I really write if I don't know parts of speech or rules of grammar? Can I really rap (yeah, I did that in high school) if I don't know iambic pentameter.  

It's kinda like when that teacher tells you that you need to understand quadratic equations to be a good athlete in sports like baseball, or basketball, or for me, volleyball, but then you find out, really you don't.  

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