Synthetics only take you so far though. Real data almost always has unusual data (outliers), or the data will violate various assumptions that you've made along

Synthetics only take you so far though. Real data almost always has unusual data (outliers), or the data will violate various assumptions that you've made along the way. In many cases there is no way to know ahead of time how the data will break your model. Which is why monitoring for model drift is so important.