What's the biggest lesson you've learned from a mistake you made?

Avoid defensive posturing and self aggrandizing. Avoid examples of not protecting the company's assets, or compromizing the safety of the workplace.

I was training a recruit. I told them what to do and how to it, but didn't explain why each step was important. They didn't understand the full impact each step had on the business, and as a result, their quality of work didn't meet expectations. Since I was the one training them, the responsibility for their quality of work fell on my shoulders. Now, any time I am assigning any task, I preface the objective of the work before I assign the tasks and how to get the work done. I learned this helps our staff take more pride in their work, and a part of something bigger.