Deals - system errors and system deviations - happen because people make mistakes.

If you sit in front of a scope long enough or stand in the tower long enough, you will make a mistake. Maybe, lots of mistakes. This is not because you are a bad person or a bad controller - it's because you're human.

Whether your mistakes turn into deals depends on two things: luck (or the lack thereof) and how your mistake relates to what's going on around you and in the air.

Like the girl who gets pregnant her "first time", you may just be unlucky. Your very first mistake may be a whopper -  it might even be your last as a controller.

Some mistakes made one day without consequence might be disasterous on another. Ever get a callsign wrong? What were the results? Although I made numerous callsign errors over the years, it never led to a deal. Many deals, however, have happened because of confused callsigns. My mistakes just happened at "the right time."

So, what are we to do? As with any human endevour, we do the best we can, then hope for a bit of luck. Work your traffic always as if lives depended on it - they do, of course - and when mistakes do crop up, acknowledge them, learn from them and then put them behind you. Don't waste time on self-doubt and stay focused on your task: to provide the best ATC service humanly possible.