I had a great day at work today!  We are working on some pretty complex accounting, and I've had to do a lot of prep at night. 
That's really awesome, what makes it so complex?
There are many different variables that need to be taken into account-- things that I don't usually deal with on a day to day basis.  But my extra prep at night has made it so that it's seeming easy.
Well that's really great that you were able to prepare so much, obviously you know what you're doing! Do you usually have to prep so much?
Not usually; this is an unusual case!