I find I am my own worst enemy, as sometimes I tend to allow myself to get anxious over a task/obstacle,etc before I actually start it. After the task is completed, I almost ALWAYS feel silly for having "built it up in my mind" so much ahead of time. So with new challenges, I try to remind myself that it isn't as bad as it seems, so just dig in and do it. It's often over before you know it, and wasn't such a big deal.
