To my understanding simple regression models worked pretty well the first time they were used. My laymans understanding is that the prediction of a simple model

To my understanding simple regression models worked pretty well the first time they were used. My laymans understanding is that the prediction of a simple model of the system like a stockmarket becomes unusable once there is a feedback loop from the model to the system. I.e. enough users using the same model that the model starts to affect prices.