Sometimes, it's hard to tell what voice to use when telling your story. Sometimes a character's voice just hits us and we think it's the best possible perspective from which to tell our story - but maybe it's not. And sometimes, we forget to even ask these questions.
Write a story twice. In the first story, write from the perspective of someone who thinks very slowly and analyzes every detail. In the second story, write from the perspective of someone who is always moving and hardly thinking.
Bonus points for difficulty go to those who write in the third person perspective and who don't base their characters' entire personas on the way in which they think.
The goal here is to not only write the story in two voices but after writing them, to identify which is the better story. Sometimes it will be the story that doesn't come naturally to you, because you've had to work harder and pay more attention to what you were writing.