Reply to Question about making the "perfect" mix

So I'm making a little longer mix than I'm used to and doing more dj'ing techniques.

How can I make the mix perfect without the insanely high levels of frustration? In other words I don't want to have just made the entire mix perfect then on the last song, mess up the transition or do something I hadn't intended to do then have to start from scratch.

Or this all part of being a dj? Being able to improvise and do things correctly on the fly.