Sunny’s not the first one to confuse cause and effect. Happens to the best of us.

@JustTheBast  
Also, I am sure even you would experiment with bashing a door with your head if you literally had no idea how to open it, and no one ever told you how to open it. That is the thing with experimentation my friend: no one truly knows what will happen, and they don’t know the steps to go through with it. We take our vast knowledge for granted sometimes, but there were many points throughout history when we were really just making numerous educated guesses (or sometimes even fumbling into the correct answer) to get the correct results. To this day there are still many scientists that are experimenting with things, trying to find the correct answer through trial and error. I would compare SUnny’s initial plan to basically be a initial hypothesis in this way: it was her guess as to what could happen based on her pre-existing knowledge (which, to be fair, wasn’t much). She tested her hypothesis through experimentation (largely getting the crystals and trying to unite them), before getting the final result.

To this I will say, honestly it makes sense that her plan was backwards. Sunny didn’t have the knowledge of how magic truly worked in Equestria, since no school taught that sort of thing and such knowledge was omitted from all history books (after all, if someone knew about it, then one of Sunny’s friends would have brought up the error in her logic). Considering the crystals were literally Sunny’s only lead into bringing back harmony and magic in Equestria, it is understandable why she would not think about trying to unite the various species at the beginning. Finally, even with that said, Sunny’s main goal wasn’t to restore magic, but rather to unite the various tribes and eliminate the discrimination that was taking place across the various lands. The restoration was just as side effect of that goal, since Sunny assumed that the ponies would only truly get along if their magic was restored. So, in the end, Sunny’s logic did end up being backwards, but only because she didn’t understand how magic worked in the first place (because nopony knew that), and her main goal of uniting everypony ended up being the very thing that brought back the magic as well.

@Setsugekka  
Ah, but it didn’t work, did it? Even when they had all three crystals and an Earth Pony, Unicorn, and Pegasus combined them in a receptacle specially made for them, it still did nothing. It wasn’t until Sunny realised that she had gone about things the wrong way around that everything started working right.
 
That aside, a dumb thing that “works” can still be dumb. Opening every door by ramming it with your head, until it pops open or someone opens it to see who’s hammering on it, is still a dumb way of opening doors, even though the end result is what you wanted — because it costs you way more than you gain, and an easier and less costly way is both available and well-known.

If it’s dumb but works, then it’s not dumb

That’s because Sunny had more of a goal than a plan. Benjamin “Motherfucking” King agrees.

That’s the thing about plans. They don’t usually go exactly the way you want and you usually have to improvise.

And I have nothing against this as long as the plan still worked.