With each thought the probability you will think additional matching or similar thoughts increases. Thus, the more you think a particular thought, the more likely it becomes you will think that thought again.
This particular phenomenon is the result of your thoughts defining your vibration which in turn defines your thoughts and thus as you think any given thought, your vibration then begins to match its energy value, harmonization, thereby resulting in the production of additional matching thoughts. Therefore, when choosing your thoughts in the present, you should try to choose thoughts you want to think again in the future.