Years ago I heard someone, possibly on NPR's Fresh Air, talking about how thoughts were a lot like food: just as we can make decisions about what we eat - "no, I am not going to eat that (now|today|ever)" - we can also learn to identify thoughts that have negative effects on us and when they happen we can choose not to think them.

At the time, this sounded a bit fanciful and just a bit ridiculous to me. Over the decades since, it has come to be one of my foundational philosophies. Obviously, I am unable to stick to it all the time, just as I sometimes eat food that I know is going to make me feel bad. But it's there as a guiding principle, all the time.

Yup, I've realized similar. "You are what you eat" and also "You are what you think". But like you said, it's not about scrutinizing every single thing you think/eat but more about recognizing patterns and seeing if those patterns are aligned with your own values.