So now let's delve into what's actually happening in the brain. Let me begin with a story. Lolo Jones was an Olympic hurdler favored to win the 2008 Olympics. She was in the finals, leading at the ninth of 10 hurdles. In an interview with Time magazine, she revealed, "I was in the middle of a race, and at one point, I realized I was winning. It wasn't like, 'Oh, I'm about to win the Olympic gold medal.' It just seemed like another race. Then, at a certain point, I started noticing that I was telling myself to make sure my legs were snapping out. That's when I hit the hurdle. So, I overtried."

The idea here isn't that she had thoughts; it's that she got caught up in thinking. She became entangled in her thoughts and, quite literally, tripped herself up. This is a fairly common process. About half of our time is spent daydreaming or getting lost in our experiences. This can be seen as a continuous cycle of daydreaming and stress, with addiction at the far end.

Given that we do this so frequently, we can study this phenomenon in the brain. This phenomenon is now referred to as the default mode network, aptly named because it's where our minds tend to default to. I'll focus on a specific part of the brain: the posterior cingulate, located at the back of the brain.

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