A sprint starts and you feel unsure or overly sure of being able to complete all the work in that sprint. And depending on that you crank at the start working long hours in stress of not getting done in time or not enough focus (too much twitter) thinking you have it under control only to stress at the end of the sprint! It would be as if I started out for a jog not knowing how long the route was in a full sprint. I need to pace myself to do it well.

This chart has helped me a ton to not only help pace myself but to simplify what I track. Joel Wenzel has a post that covers the using his spreadsheet to do a simple burndown. He points out in the post that you just need to focus on marking tasks Complete and not trying to track how complete, or how long did it really take.

His post makes it super clear and I added this video as well.