Starting in iOS 7, the iPhone and iPad had something called the "control center," which was a little tab at the bottom of the screen that allows you to easily turn on the Bluetooth, control your mp3s, or whatever without having to go to their individual app:

It's useful, yes, but at the time and still occasionally now I become annoyed because the way to access it is to swipe up from the bottom of the screen. Except often when I'm reading the newspaper, books, etc. I'm constantly trying to swipe up and instead I get this control center. Eventually I got used to it and it's not too much of an issue now.

With the most recent iOS 9, they added this "split screen" feature that allows you to use to apps at once. That sounds amazing for me because I'm constantly switching between my flashcard app and notebook app when I'm studying. Except there's a basic design flaw. You have to swipe from the right of the screen toward the left to open it. That's exactly the same motion as when you have to delete something, like an email or note. It's not like the control center; to scroll down it doesn't matter where my finger is on the screen, so I trained myself not to touch the lowest part so as not to open the control center. In this, both motions are on the far right. And why do that? Why not make it the left side of the screen? There's literally no motion on that side. Why disregard that?