For all intents and purposes, it's safe to say that you are your thoughts.
The place you are in, the people you have around, the activities you do or don't profoundly influence your brain's default state. They define what your mind jumps to in its default resting state.
Spend enough time in a shitty place, with toxic people, without any activity to distract you, and the quality of your thoughts will degrade. That's what happened to many people thanks to the lockdowns — it's called situational depression.
How do you escape that? I don't know. It's something I am still exploring.