The first few minutes are the hardest.
This doesn't make much sense to me. Naturally, I assumed that when I was fresh and just starting out, the exercise would seem easier than later when I was more tired. But, the opposite is true! When I first start a run, my thought process has been "Oh crap! If I am this achy and winded after only 3 minutes, how in the world will I ever run for 30. It's impossible! Ahhhhhhhhhh!" It's the same thought I have when I begin a workout on the elliptical. My thighs are on fire when I start. They burn so bad that I think about quitting in order to spare myself 30 minutes of torture. But after a few minutes, that burning sensation fades, and I can complete the workout feeling much better. And sometime after the first bit of running is when my body becomes easier to move, my breathing easier to maintain.
Now I am trying to force a different thought into my mind at the beginning of a run. "Come on now, you know your body is going to settle down in a few minutes. Just push through this first part and believe that it will become easier."