Stanley McChrystal

 "...you should have running list of three people that you are watching: someone senior to you that you want to emulate, a peer who you think is better at the job than you are and who you respect, and someone subordinate who's doing the job you did - one, two, or three years ago - better than you did it. If you just have those three individuals that you're constantly measuring yourself off of, and you're constantly learning from them, you're going to be exponentially better than you are." - Stanley McChrystal