"Unfortunately, during my career, I've made many mistakes. However, I make sure that I learned from these and try not to repeat them. An example of this occurred early in my career when I was required to assist a user with an unfamiliar problem. Rather than acknowledge this and seek assistance or research the issue, I plowed ahead and tried to guess at the answer. This not only exasperated the situation, making the problem worse and frustrating the user, but it resulted in me having to seek assistance anyway. What I learned from this is that when I encounter a situation, I'm not familiar with, I immediately acknowledge this, seek help, and document the solution to the problem so I will be able to resolve it myself next time."
