In the jobs that I enjoyed doing, when I hit something new, if I found I was sure I could handle it I immediately handed it on to a junior; if I was unsure of myself and worried about whether I could produce, I got on with it. If you are always challenged, you will be always unsure, always worried. If you aren't challenged, life is just too dull. Learning new things is fun, but you can never be sure you will manage to understand them until you have learnt the critical parts, so unsureness must be a sign that you are having fun.

Now that I'm pretty much retired I don't hit enough situations where I'm not sure I'm up to what I need to do. Maybe I need to unretire.