In My experience, there is no such thing as luck. ~ Obi Wan Kenobi
Its all about momentum. Most matches are won or lost due to shifts in momentum - and how we react to those shifts. Each shift in momentum has what is called a precipitating event, which either shifts the momentum in your favor, or out of your favor. Recognizing when these precipitating events occur is half the trick to learning whether or not the momentum is in or out of your favor.
Picture a situation where you have run 2 or 3 racks in succession only to scratch on the 8 ball to give your opponent and easy ball in hand shot to win a game. Your reaction to that can make all the difference as to whether or not you get the pendulum to swing back in your direction. Your opponent's reaction to that same event is also important. He can remain calm and focused on running some racks back on you - or - he can allow the excitement caused by your error to generate feelings of over-confidence.
We've all been on both sides of that.
It's the same thing with trends and slumps - they have precipitating events as well. This works in both directions - positively and negatively. If you start getting those opportunities to win, there will be a precipitating event that will start that shift in the momentum - you just have to recognize it and take full advantage of it.
Chances are, you are already getting these opportunities, you just have not been able to find a way to ride the wave of momentum yet. Many times, this is the case when players believe that momentum only shifts within the physical occurrences on the table. Momentum also shifts psychologically - and you need to be prepared for that.
Psychological Momentum - the positive or negative change in cognition, affect, physiology, and behavior caused by an event or series of events that affects either the perceptions of the competitors or, perhaps, the quality of performance and the outcome of the competition. Positive momentum is associated with periods of competition, such as a winning streak, in which everything seems to ‘go right’ for the competitors. In contrast, negative momentum is associated with periods, such as a losing streak, when everything seems to ‘go wrong
Here are some great articles that I have found on this subject. The articles are geared towards other sports, but the lessons can easily be applied to the game of pool.
Riding The Wave of Momentum - by Jeff Greenwald
Leyton Hewitt - Confidence and Momentum in Tennis ~ By Patrick J. Cohn