Trying not to think about something guarantees that it is never far from your mind. This leads to a second problem: When you try to push a thought away, and it keeps coming back to your mind, you are more likely to assume that it must be true. Why else would the thought keep resurfacing? We trust that our thoughts are important sources of information. When a thought becomes more frequent and harder to pull yourself away from, you will naturally assume that it is an urgent message that you should pay attention to. This cognitive bias seems to be hardwired in the human brain. We estimate how likely or true something is by the ease with which we can bring it to mind. This can have unsettling consequences when we try to push a worry or desire out of our minds.
— The Willpower Instinct (Kelly McGonigal), Loc. 3251–7