Long-running agents fail because they drift off the distribution they were trained on, and degrade further the farther out they get.

Chief Scientist at Google DeepMind and Google Research

Um, and sometimes that's because the model is trying to do something it doesn't have a lot of experience doing. So it's been trained on a whole set of things and as soon as you get a little bit off the distribution of things it knows how to do then like most machine learning models it will you know its performance will suddenly will start to degrade and the farther you get off the comfort zone of what it knows how to do the the more likely it is to to not work as well.