The reality of the unseen realm changes everything.
Thoughts are not purely private. They exist in a dimension at least as powerful as our sensory dimension. Likely much more powerful.
Whether or not we can generate original thoughts from this plane, our thoughts are certainly more than just that. They go out into their own dimension, doing and begetting what’s in their nature to do and beget.
But they also often come from that dimension into our heads. They do not all originate in us. That is why they must be examined, ‘taken captive’, blocked, rejected, discarded, immediately implemented, or carefully dealt with as appropriate.
Things outside of us can send thoughts into us. We can do the same. We are swimming in a sea of thoughts, of mostly unknown origin.
All serious battles begin in the mind. We win or lose based on how we master or are mastered by thoughts.