The biggest thing I learned is how many years it really takes to get a good grasp on all the aspects of options.
It's fairly straightforward to learn the greeks, theory and even practice, but until you have positions on and watch the market go through many different iterations of movement - it's hard to know how you will react and how your positions will behave and react.
For instance...even though you may have complete price predictability and know and understand exactly what you will do during certain moves, there may be no one there to make the market. Then what will you do.
It's amazing how often you think you've become very comfortable with what you're doing and then how quickly you can become uncomfortable again.