Here's the simple stream of consciousness reply:
The word suffering sucks. It has too little and too much meaning.
You can't get rid of the fact that the world isn't set up with you in mind.
You can't get rid of the fact that you have to deal with other people.
You can understand that though, and you can deal with it. You can find a way to not just react to suffering, but to understand your relationship to it.
You can get pissed at something for a second, then recover yourself and find some equanimity.
You can feel pain and know that that pain is just temporary.
You can recognize that you can't control the world around you, and find some peace in that understanding.
So, that's the gist of my problem with that third rule. Very few of us will devote our lives to the practice and study of mindfulness, but that's not necessary. We don't have to end something or control it, we only need to learn how to understand how transient and unimportant it really is.
Suffering isn't the first feeling we get when something negative happens, it's our prolonged reaction to the event, our dwelling on the event.
You don't need to end suffering, you just have to not let it get too comfortable before you kick it out.