Cognitive Behavioral Therapy (CBT) is noted for developing the ABC model of behavior. One of the many versions of the model proposes an Activating Event (an experience or event that sets off the cascade), Beliefs (we evaluate what we've experienced, either rationally or irrationally), and Consequences (what happens in our mind or emotions, or actions we take as a result).
We start with a SITUATION (A) and end up with a FEELING (C) but often we miss the THOUGHT (B) that links them.
So, how does that happen? Automatic emotional reactions occur because we have a running commentary, a steady stream of thoughts that we barely notice, if at all. These thoughts dictate how we end up feeling. For example:
A You run into a good friend at the coffee shop before work. She's with other people and barely notices you.
B You think, "she hates me, just like so many others hate me."
C You feel sadness bordering on depression.
But it doesn't end there. It's a cycle. Now that you're in a sad mood, it may color your perception of the next event you encounter when you get to work. Your boss asks you to fix a small mistake you made, and before you know it, you are at C deeper sadness, skipping over the interpreting thought, "He thinks I'm bad at what I do, and I am." By the time our friend texts us to say, "Sorry I didn't get a chance to say hello. I was tied up in a conversation about my career," we've already been caught in a very low mood all day.
Mindfulness' strength is in helping us to see B more clearly, by giving us the room to not be so quickly reactive. And over time the event does not have to jump to emotional distress.