Many years ago I was so sure that a new consultancy that I had started was going to win a big tender and set the business on its path that I left my old job so that I would have time to deal with the work coming from the tender. Guess what happened? We managed to lose the un-losable tender, which of course then presented some fairly major challenges. Not to mention the disappointment! I have since then developed a healthy circumspection about tenders, never expecting a thing, but when we do win one I feel excited (and a bit triumphant).
How many times have you been excited about a concert or forthcoming event, talking it up in your mind, only to be disappointed with the end result? How often have you felt sure your flight will take off on time, and then discovered that the flight has been delayed.
The thing about being totally sure of something is that, when it happens you feel reasonably satisfied, but if it doesn't you can end up feeling disappointed or worse. However, if you accept in any circumstance that any outcome might be possible, you stop setting yourself up for disappointment and start getting creative about what to do with all possible outcomes.
The idea here is not to flat-line with emotions, expect nothing and cut all anticipation out of your life, but rather to remain open to all possibilities, all of the time. You will be amazed at how your creativity levels soar.