What about form and convention and structure?

Of course the conventions seem arbitrary and ridiculous even to me sometimes. I'm talking here about literary and grammatical conventions. Tonight I was watching "Everwood" and Andy was writing a letter to his dead wife. The structure of the letter struck me as silly and random. What difference could it possibly make if he just wrote: "Dear Julia, It made me mad when you cheated on me. Love, Andy" in one line like that? Let's set aside the fact that the wife is deceased and focus on the letter-writing genre, which is largely dead, I understand, but this idea can be applied to email as well, if the emailer is the sort of emailer that I am. I write emails in the same format as I would write a letter because I am a slave to conventions. Indeed, I am like a religious zealot when it comes to The Rules of Grammar. But tonight, during "Everwood," I had a sort of epiphany. I've been heading in this direction for a couple weeks, ever since I had a similar realization about public restrooms. The problem is that I'm afraid these conventions are built on a false foundation, and since I've pretty much been living my life in a tribute to these conventions, what do I have if I don't have these conventions to structure my writing, my reading, and my life? What if Andy (the husband, not the "Everwood" character) is right and literary criticism if crap? What if a story is just a story? What will I do then?